Camera accessory

ABSTRACT

An accessory mount can be inserted through the camera body mount without any of the first through third tabs being hindered by any of three camera body-side tabs at the camera body mount, as long as the accessory mount is inserted into the camera body mount at a correct interlock phase. The first tab, the second tab and the third tab extend over varying lengths along the circumferential direction. The first tab extends over a greatest length along the circumferential direction among the first through third tabs. The third tab extends over a smallest length along the circumferential direction among the first through third tabs. The accessory mount includes a restricting member disposed near the third tab, a fitting portion used to align an optical axis of the accessory mount with an optical axis of the camera body, and a lock pin hole through which a lock pin, retractably disposed at the camera body, is inserted so as to lock the camera accessory in a fully mounted state. The restricting member is disposed at a position assumed on a side substantially opposite from the lock pin hole across the fitting portion.

INCORPORATION BY REFERENCE

The disclosures of the following priority applications are hereinIncorporated by reference:

Japanese Patent Application No. 2010-198864 filed Sep. 6, 2010

Japanese Patent Application No 2011-135245 filed Jun. 17, 2011

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a camera accessory that can bedetachably engaged with a camera body equipped with a camera body mountassuming a bayonet structure.

2. Description of Related Art

A camera accessory, such as an exchangeable lens, and a camera bodyassuming structures that allow them to be detachably engaged with eachother via a mount system adopting a bayonet structure are known in therelated art. Such a camera accessory and a camera body are engaged witheach other by first inserting a camera accessory mount through a camerabody mount at the correct interlock phase and then rotating the cameraaccessory along a predetermined direction (mounting direction) aroundthe incident light optical axis. The camera accessory can be dismountedfrom the camera body by first rotating the camera accessory mounted atthe camera body along a direction (dismounting direction) opposite fromthe mounting direction and then pulling the camera accessory forwardrelative to the camera body.

Japanese Laid Open Patent Publication No. H3-229229 discloses a systemthat includes a camera accessory and a camera body structured asdescribed above, whereby a projecting portion formed at the cameraaccessory comes in contact with a side end of a tab at the camera bodymount when the camera accessory is being mounted at or dismounted fromthe camera body, so as to restrict the range of rotation of the cameraaccessory along the mounting direction or the dismounting direction.

SUMMARY OF THE INVENTION

In the mount system disclosed in the patent literature cited above, theportion (restricting portion) that restricts the rotation range bycoming into contact with a side end of a tab at the camera body mountassumes a position close to a retainer lock groove via which the cameraaccessory is held fast. For this reason, backlash between the cameraaccessory and the camera body centered on a camera body-side pininserted through the lock groove, which is attributable to the clearanceformed as the camera accessory is mounted at the camera body, cannot becompletely prevented via the restricting portion.

A camera accessory that can be detachably mounted at a camera body thatincludes a camera body mount, and includes an accessory mount assuming abayonet structure with a first tab, a second tab and a third tab setover intervals in a circumferential direction running along acircumference of a circle with a predetermined diameter and projectingfrom the circumference along a radial direction, according to a firstaspect of the present invention, the accessory mount can be insertedthrough the camera body mount without any of the first through thirdtabs being hindered by any of three camera body-side tabs at the camerabody mount, as long as the accessory mount is inserted into the camerabody mount at a correct interlock phase; the first tab, the second taband the third tab extend over varying lengths along the circumferentialdirection; the first tab extends over a greatest length along thecircumferential direction among the first through third tabs; the thirdtab extends over a smallest length along the circumferential directionamong the first through third tabs; the accessory mount includes arestricting member disposed near the third tab, a fitting portion usedto align an optical axis of the accessory mount with an optical axis ofthe camera body, and a lock pin hole through which a lock pin,retractably disposed at the camera body, is inserted so as to lock thecamera accessory in a fully mounted state; and the restricting member isdisposed at a position assumed on a side substantially opposite from thelock pin hole across the fitting portion.

According to a second aspect of the present invention, in the cameraaccessory according to the first aspect, it is preferable that when thefirst through third tabs are rotated along the circumference in a firstrotating direction in order to mount the accessory mount, having beeninserted at the correct interlock phase, at the camera body mount, therestricting member comes into contact with a side end of one camerabody-side tab among the camera body-side tabs, thereby restricting arange of rotation in the first rotating direction; and when the firstthrough third tabs are rotated along the circumference in a secondrotating direction opposite from the first rotating direction in orderto dismount the accessory mount from the camera body mount, therestricting member comes into contact with a side end of a camerabody-side tab different from the one camera body-side tab, therebyrestricting a rotation range in the second rotating direction.

According to a third aspect of the present invention, in the cameraaccessory according to the first aspect, it is preferable that insertionof the accessory mount through the camera body mount is disallowed ifthe accessory mount is positioned at a phase other than the correctinterlock phase, with at least two tabs among the first tab, the secondtab and the third tab coming into contact with at least two of thecamera body-side tabs.

According to a fourth aspect of the present invention, in the cameraaccessory according to the first aspect, it is preferable that the firsttab at the accessory mount having been inserted at the correct interlockphase and engaged with the camera body mount overlaps a camera body-sidetab assuming an uppermost position when the camera body is set with alongitudinal orientation achieved by rotating the upright camera bodyassuming a lateral orientation by approximately 90°.

According to a fifth aspect of the present invention, in the cameraaccessory according to the first aspect, the first tab, the second taband the third tab may be fixed to a main body of the camera accessory.

According to a sixth aspect of the present invention, in the cameraaccessory according to the first aspect, the first tab, the second taband the third tab may be rotatably disposed so as to be allowed torotate along the circumferential direction relative to a main body ofthe camera accessory.

According to a seventh aspect of the present invention, in the cameraaccessory according to the first aspect, it is preferable that the firsttab, the second tab and the third tab are made up with a tab presentover an angular range of 56.5° to 115°, a tab present over an angularrange of 172.5° to 214.5° and a tab present over an angular range of272° to 343.5° at the accessory mount engaged with the camera bodymount, along a clockwise direction relative to a nine o'clock directionviewed from a rear side of the accessory mount.

According to a eighth aspect of the present invention, in the cameraaccessory according to the first aspect, it is preferable that anglesdefining circular arcs representing lengths of the first tab, the secondtab and the third tab extending along the circumferential direction arerespectively 71.5°, 58.5° and 42°.

According to a ninth aspect of the present invention, in the cameraaccessory according to the seventh aspect, it is preferable that whenthe first tab, the second tab and the third tab are rotated along thecircumferential direction by 40.5° in order to engage the accessorymount, having been inserted at the correct interlock phase, with thecamera body mount, the accessory mount becomes engaged with the camerabody mount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematically illustrating a camera body withexchangeable lenses and a photographic lens that can be detachablymounted at the camera body, in conjunction with which the presentinvention may be adopted.

FIG. 2 is a perspective schematically illustrating the structure of thebody mount, viewed along a diagonal direction from a front rightviewpoint relative to the camera body.

FIG. 3 is a perspective schematically illustrating the structure of theaccessory mount, viewed along a diagonal direction from a rear leftviewpoint relative to the photographic lens.

FIG. 4 indicates the position at which a restricting member is disposed.

FIG. 5 indicates the positions of the body-side tabs and the body-sidegaps at the body mount viewed from the front side of the camera body.

FIG. 6 indicates the positions of the accessory-side tabs and theaccessory-side gaps at the accessory mount viewed from the rear side ofthe photographic lens.

FIG. 7 shows a specific state of interference (state of overlap) betweenthe body-side tabs and the accessory-side tabs.

FIG. 8 shows a specific state of interference (state of overlap) betweenthe body-side tabs and the accessory-side tabs.

FIG. 9 schematically illustrates the body-side first tab expanded alongthe circumference in a view taken from the outer side along the radialdirection.

FIGS. 10A through 10F illustrate how the state of engagement between theaccessory-side second tab and the body-side second tab changes as thephotographic lens is mounted and dismounted.

FIG. 11 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 12 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 13 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 14 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 15 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 16 illustrates the relationship between the body mount and theaccessory mount that will manifest if an excessive external force isapplied to the photographic lens along the direction matching that ofgravitational force.

FIG. 17 indicates the contact points PD and PU and the distance LSassumed when the camera body is in a lateral orientation.

FIG. 18 indicates the contact points PD and PU and the distance LSassumed when the camera body is in a longitudinal orientation.

FIG. 19 indicates the contact points PD and PU and the distance LSassumed when the camera body is in another longitudinal orientation.

FIGS. 20A and 20B present an example of a variation.

FIG. 21 illustrates the variation example.

FIGS. 22A through 22D illustrate the variation example.

FIG. 23 is a perspective schematically illustrating a camera body withexchangeable lenses and a photographic lens that can be detachablymounted at the camera body, achieved in a second embodiment.

FIGS. 24A and 24B present a perspective schematically illustrating thestructure of the body mount 100, viewed along a diagonal direction froma front right viewpoint relative to the camera body.

FIG. 25 is a perspective schematically illustrating the structure of theaccessory mount, viewed along a diagonal direction from a rear leftviewpoint relative to the photographic lens.

FIGS. 26A and 26B indicate the position at which a restricting member isdisposed.

FIG. 27 indicates the positions of the body-side tabs and the body-sidegaps at the body mount viewed from the front side of the camera body.

FIG. 28 indicates the positions of the accessory-side tabs and theaccessory-side gaps at the accessory mount viewed from the rear side ofthe photographic lens.

FIG. 29 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 30 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 31 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 32 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 33 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 34 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 35 shows a specific state of interference (state of overlap)between the body-side tabs and the accessory-side tabs.

FIG. 36 illustrates how the accessory mount may swing relative to thecamera body mount when there is a significant clearance between theinner circumferential surface of the camera body mount and the fittingportion of the accessory mount.

FIG. 37 illustrates a range of the phase that the restricting member mayassume in a fully mounted state.

FIG. 38 is a graph indicating a range of the phase that the restrictingmember may assume in a fully mounted state.

DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

In reference to FIGS. 1 through 19, the camera accessory, the accessorymount, the camera body and the body mount achieved in a first embodimentof the present invention are described. FIG. 1 is a schematicperspective of a camera body 1 with an exchangeable photographic lens 2that can be detachably mounted at the camera body 1, in conjunction withwhich the present invention is adopted. A shutter release button 4, animage sensor 5 and a control circuit 6 that controls various units ofthe camera body 1 are disposed at the camera body 1. Reference numeral 3indicates a photographic optical path through which a subject imagedeparting the photographic lens 2 is guided to the image sensor 5.

On the front side of the camera body 1, a body mount 100 assuming abayonet structure is disposed via which a camera accessory, e.g., thephotographic lens 2 or a converter lens used to adjust the focal length,is mounted at the body mount 100. On the rear side of the photographiclens 2, a lens mount, i.e., an accessory mount 200, via which thephotographic lens 2 can be detachably mounted at the body mount 100, isdisposed. It is to be noted that FIG. 1 does not include detailedillustrations of the structures adopted in the body mount 100 and theaccessory mount 200. In addition, in the description of the embodiment,the front side (toward the subject) of the camera body 1 on which thephotographic lens 2 is mounted is referred to as “forward” and the rearside of the camera body 1 where the image sensor 5 is mounted, isreferred to as “rearward”. Atop-bottom direction, a left-right directionand a front-rear direction are defined as indicated in FIG. 1 for thecamera body 1. FIG. 1 shows that the top-bottom direction relative tothe camera body 1 matches the vertical direction. The attitude of thecamera 1 shown in FIG. 1 is referred to as an upright attitude or alateral orientation. The attitude of the camera body 1 assumed byrotating the camera body with the lateral orientation by 90° clockwiseor counterclockwise viewed from the front side is referred to as alongitudinal orientation.

—Body Mount 100—

FIG. 2 is a schematic perspective illustrating the structure of the bodymount 100 viewed along a diagonal direction from a front right viewpointrelative to the camera body 1. The body mount 100 adopts a bayonetstructure that includes three tabs (body-side tabs) set apart from oneanother along the circumferential edge of a circular opening(photographic optical path) at the camera body 1, each projecting inwardfrom the outer side of the opening circumference. Among the threebody-side tabs, the body-side tab located at the uppermost position isreferred to as a body-side first tab 110, the body-side tab located nextto the body-side first tab 110 along the counterclockwise direction inthe figure is referred to as a body-side second tab 120 and thebody-side tab located next to the body-side second tab 120 along thecounterclockwise direction is referred to as a body-side third tab 130.

The space created between two consecutive body-side tabs, through whicha tab (accessory-side tab) at the accessory mount 200 passes when thephotographic lens 2 is being mounted or dismounted as explained later,is referred to as a body-side gap. The body-side gap present between thebody-side third tab 130 and the body-side first tab 110 is referred toas a body-side first gap 151, the body-side gap located next to thebody-side first gap 151 along the counterclockwise direction in thefigure is referred to as a body-side second gap 152 and the body-sidegap located next to the body-side second gap along the counterclockwisedirection is referred to as a body-side third gap 153.

The surface of the body-side first tab 110 facing forward is referred toas a front surface 113, the counterclockwise side end of the body-sidefirst tab 110 facing the body-side second gap 152 is referred to as afirst side end 111, and the clockwise side end of the body-side firsttab 110 facing the body-side first gap 151 is referred to as a secondside end 112. Likewise, the surface of the body-side second tab 120facing forward is referred to as a front surface 123, the side end ofthe body-side second tab 120 facing the body-side third gap 153 isreferred to as a first side end 121 and the side end of the body-sidesecond tab 120 facing the body-side second gap 152 is referred to as asecond side end 122. The surface of the body-side third tab 130 facingforward is referred to as a front surface 133, the side end of thebody-side third tab 130 facing the body-side first gap 151 is referredto as a first side end 131, and the side end of the body-side third tab130 facing the body-side third gap 153 is referred to as a second sideend 132. It is to be noted that the first side ends 111, 121 and 131 aretab ends formed facing toward a mounting direction, to be described indetail later, whereas the second side ends 112, 122 and 132 are tab endsformed facing toward a dismounting direction (opposite the mountingdirection).

It is to be noted that, although not shown in FIG. 2, the surface of thebody-side first tab 110 facing rearward is referred to as rear surface114. Likewise, the surfaces of the body-side second tab 120 and thebody-side third tab 130 facing rearward are respectively referred as arear surface 124 and a rear surface 134.

Reference numeral 101 indicates a body mount reference surface. The bodymount reference surface 101 is a ring-shaped flat surface formed so asto face toward the front side. As the photographic lens 2 is mounted atthe camera body 1, the body mount reference surface 101 comes intocontact with an accessory mount reference surface 201 of the accessorymount 200, which is to be described in detail later, thereby regulatingthe position assumed by the photographic lens 2 along the front-reardirection. Reference numeral 102 indicates an inner circumferentialsurface of the cylindrical body mount 100. The inner circumferentialsurface 102, which interlocks with a fitting portion of the accessorymount 200, to be detailed below, is used as a reference surface, inreference to which the optical axis of the photographic lens 2 isaligned with the optical axis of the camera body 1 (the central axis ofthe photographic optical path 3). Reference numeral 161 indicates a pinhole through which a pin (not shown) projects out or retracts in. Thepin projecting out through the pin hole 161 disallows rotation of themounted photographic lens 2 relative to the camera body 1.

—Accessory Mount 200—

FIG. 3 is a perspective schematically illustrating the structure of theaccessory mount 200 viewed along a diagonal direction from a rear leftviewpoint relative to the photographic lens 2. It is to be noted thatFIG. 3 shows the accessory mount 200 with the photographic lens 2 fullymounted at the camera body 1 (mounting complete state), i.e., in aphotographing-enabled state. This means that the top-bottom/left-rightorientation of the accessory mount 200 shown in FIG. 3 matches thetop-bottom/left-right orientation of the camera body 1. Unlessspecifically noted, the following description is given by assuming thatthe top-bottom/left-right orientation of the accessory mount 200 is theorientation in the mounting complete state.

The accessory mount 200 adopts a bayonet structure that includes threetabs (accessory-side tabs) set apart from one another along thecircumferential direction, each projecting from the inner side of thecircumference toward the outer side of the circumference. Among thethree accessory-side tabs, the accessory-side tab located at theuppermost position is referred to as an accessory-side first tab 210,the accessory-side tab located next to the accessory-side first tab 210along the clockwise direction in the figure is referred to as anaccessory-side second tab 220 and the accessory-side tab located next tothe accessory-side second tab 220 along the clockwise direction isreferred to as an accessory-side third tab 230.

The space created between two consecutive accessory-side tabs, throughwhich a body-side tab passes when the photographic lens 2 is beingmounted or dismounted as explained later, is referred to as anaccessory-side gap. The accessory-side gap present between theaccessory-side first tab 210 and the accessory-side second tab 220 isreferred to as an accessory-side first gap 251, the accessory-side gaplocated next to the accessory-side first gap 251 along the clockwisedirection in the figure is referred to as an accessory-side second gap252 and the accessory-side gap located next to the accessory-side secondgap along the clockwise direction is referred to as an accessory-sidethird gap 253.

The surface of the accessory-side first tab 210 facing rearward isreferred to as a rear surface 213, the side end of the accessory-sidefirst tab 210 facing the accessory-side first gap 251 is referred to asa first side end 211 and the side end of the accessory-side first tab210 facing the accessory-side third gap 253 is referred to as a secondside end 212. Likewise, the surface of the accessory-side second tab 220facing rearward is referred to as a rear surface 223, the side end ofthe accessory-side second tab 220 facing the accessory-side second gap252 is referred to as a first side end 221, and the side end of theaccessory-side second tab 220 facing the accessory-side first gap 251 isreferred to as a second side end 222. The surface of the accessory-sidethird tab 230 facing rearward is referred to as a rear surface 233, theside end of the accessory-side third tab 230 facing the accessory-sidethird gap 253 is referred to as a first side end 231 and the side end ofthe accessory-side third tab 230 facing the accessory-side second gap252 is referred to as a second side end 232. The first side ends 211,221 and 231 are tab ends formed toward the mounting direction to bedescribed in detail later, whereas the second side ends 212, 222 and 232are tab ends facing toward a direction (dismounting direction) oppositefrom the mounting direction.

It is to be noted that, although not shown in FIG. 3, the surface of theaccessory-side first tab 210 facing forward is referred to as a frontsurface 214. Likewise, the surfaces of the accessory-side second tab 220and the accessory-side third tab 230 facing forward are respectivelyreferred to as a front surface 224 and a front surface 234.

Reference numeral 201 indicates an accessory mount reference surface.The accessory mount reference surface 201 is a ring-shaped flat surfaceformed so as to face rearward, and is in contact with the body mountreference surface 101 when the photographic lens 2 is fully mounted.Reference numeral 202 indicates a fitting portion. The fitting portion202 is a cylindrical portion that fits at the inner circumferentialsurface 102 of the body mount 100 and is used for reference whenaligning the optical axis of the photographic lens 2 with the opticalaxis of the camera body 1 (the central axis of the photographic opticalpath 3). Reference numeral 261 indicates a pin hole. As a pin (notshown), which projects out or retracts into the pin hole 161 at the bodymount 100, is inserted through the pin hole 261, rotation of the fullymounted photographic lens 2 relative to the camera body 1 (body mount100) becomes disallowed and the photographic lens 2 thus becomes locked.

Although not shown in FIG. 3, a restricting member 262, which limits therotation range of the photographic lens 2 (accessory mount 200) relativeto the camera body 1 (body mount 100) while the photographic lens 2 ismounted or dismounted, is disposed frontward relative to theaccessory-side second tab 220 near its second side end 222, as shown inFIG. 4. The restriction of the rotation range achieved via therestricting member 262 will be described in detail later. Therestricting member 262 may be, for instance, a headed pin screwed infrom the outer side of the accessory mount 200 along the radialdirection.

—Positions of Body-Side Tabs and Body-Side Gaps—

FIG. 5 indicates the positions of the body-side tabs and the body-sidegaps at the body mount 100 viewed from the front side of the camera body1. A reference angular position is taken along the three o'clockdirection at the body mount 100 viewed from the front side of the camerabody 1 and various angles representing the positions at which thebody-side tabs are disposed, are assumed along the counterclockwisedirection relative to the three o'clock direction. Namely, the body-sidefirst tab 110 extends over an angular range of 76° to 130°, thebody-side second tab 120 extends over an angular range of 177.5° to 226°and the body-side third tab 130 extends over an angular range of 304.5°to 15° (375°).

The sizes of the individual body-side tabs 110 to 130 can each beindicated by the corresponding angular range along the circumferentialedge of the circular opening at the body mount 100. Namely, thebody-side first tab 110 has a 54° angular range, the body-side secondtab 120 has a 48.5° angular range and the body-side third tab 130 has a70.5° angular range. Likewise, the sizes of the individual body-sidegaps 151 to 153 can each be indicated by the corresponding angular rangealong the circumferential edge of the circular opening at the camerabody 1. Namely, the body-side first gap 151 has a 61° angular range, thebody-side second gap 152 has a 47.5° angular range and the body-sidethird gap 153 has a 78.5° angular range.

Reference numeral 7 in FIG. 5 indicates an index mark at the camera body1. The index mark 7 is used as a reference mark when mounting thephotographic lens 2 at the camera body 1. The index mark 7 assumes a 90°angular position counterclockwise relative to the reference threeo'clock direction taken at the body mount 100 viewed from the front sideof the camera body 1.

—Positions of Accessory-Side Tabs and Accessory-Side Gaps—

FIG. 6 indicates the positions of the accessory-side tabs and theaccessory-side gaps at the accessory mount 200 viewed from the rear sideof the photographic lens 2. A reference angular position is taken alongthe nine o'clock direction at the accessory mount 200 viewed from therear side of the photographic lens 2 fully mounted at the camera body.Various angles representing the positions at which the accessory-sidefirst tabs are disposed, are assumed along the clockwise directionrelative to the nine o'clock direction. Namely, the accessory-side firsttab 210 extends over an angular range of 56.5° to 115°, theaccessory-side second tab 220 extends over an angular range of 172.5° to214.5°, and the accessory-side third tab 230 extends over an angularrange of 267.5° to 343.5°.

The ranges over which the accessory-side tabs 210 to 230 extend alongthe circumference of the accessory mount 200 can each be indicated bythe corresponding angular range along the circumference of the accessorymount 200. Namely, the accessory-side first tab 210 has a 58.5° angularrange, the accessory-side second tab 220 has a 42° angular range and theaccessory-side third tab 230 has a 76° angular range. Likewise, thesizes of the individual accessory-side gaps 251 to 253 can each beindicated by the corresponding angular range along the circumference ofthe accessory mount 200. Namely, the accessory-side first gap 251 has a57.5° angular range, the accessory-side second gap 252 has a 53° angularrange and the accessory-side third gap 253 has a 73° angular range.

Reference numeral 8 in FIG. 6 indicates an index mark at thephotographic lens 2. The index mark 8 is used as a reference mark whenmounting the photographic lens 2 at the camera body 1. The index mark 8assumes a 130.5° angular position clockwise relative to the nine o'clockdirection taken at the accessory mount 200 viewed from the rear side ofthe photographic lens 2 in the mounting complete state. This angle isequal to a value representing the sum of 90° and a mounting angle of40.5° to be described in detail later.

As explained earlier, the restricting member 262 is disposed frontwardrelative to the accessory-side second tab 220 near its second side end222. This means that the restricting member 262 is disposed near theaccessory-side second tab 220 extending over the shortest range alongthe circumference of the accessory mount 200 (with the smallest angularrange along the circumference of the accessory mount 200).

—Mounting the Photographic Lens 2 at the Camera Body 1—

The photographic lens 2 structured as described above is mounted at thecamera body 1 through the following procedure. It is to be noted thatthe rotational position assumed by the photographic lens 2 relative tothe camera body 1 when the axis extending along the front-rear directionthrough the center of the photographic optical path 3 of the camera body1 and the optical axis of the photographic lens 2 are aligned with eachother is to be hereafter referred to simply as an interlock phase. Whilesustaining the alignment of the axis extending along the front-reardirection through the center of the photographic optical path 3 at thecamera body 1 and the optical axis of the photographic lens 2, thephotographic lens 2 is mounted at the camera body 1 by aligning therotational position of the index mark at the photographic lens 2 withthe rotational position of the index mark at the camera body 1. When thetwo index marks are aligned, the photographic lens 2 and the camera body1 achieve a positional relation relative to each other in which thebody-side tabs 110 to 130 and the accessory-side tabs 210 to 230 do notinterfere with each other, as shown in FIG. 7, and the accessory mount200 can be thus inserted through the body mount 100 until the accessorymount reference surface 201 contacts the body mount reference surface101. The interlock phase assumed in this state is to be referred to as acorrect interlock phase. It is to be noted that in FIG. 7, showing aspecific state of interference (state of overlap) between the body-sidetabs 110 to 130 and the accessory-side tabs 210 to 230, theaccessory-side tabs are shown as fan-shaped members in a schematicrepresentation.

As the accessory mount 200 is inserted at the body mount 100 at thecorrect interlock phase, the accessory-side first tab 210 passes fromfront to back through the body-side first gap 151, the accessory-sidesecond tab 220 passes from front to back through the body-side secondgap 152 and the accessory-side third tab 230 passes from front to backthrough the body-side third gap 153. Likewise, the body-side first tab110 passes from back to front through the accessory-side first gap 251(no reference numeral appended in FIG. 7), the body-side second tab 120passes from back to front through the accessory-side second gap 252 (noreference numeral appended in FIG. 7) and the body-side third tab 130passes from back to front through the accessory-side third gap 253 (noreference numeral appended in FIG. 7), as the accessory mount 200 isinserted through the body mount 100 at the correct interlock phase.

As the photographic lens 2 is turned along the counterclockwisedirection viewed from the front side of the camera body 1 after theaccessory mount 200 is inserted through the body mount 100 at thecorrect interlock phase, the accessory-side first tab 210 takes up aposition to the rear of the body-side first tab 110, the accessory-sidesecond tab 220 takes up a position to the rear of the body-side secondtab 120 and the accessory-side third tab 230 takes up a position to therear of the body-side third tab 130. When the photographic lens 2 isturned by 40.5° relative to the correct interlock phase along thecounterclockwise direction viewed from the front side of the camera body1 as shown in FIG. 8, the restricting member 262 comes in contact withthe second side end 122 of the body-side second tab 120, therebypreventing further rotation along the counterclockwise direction. Inother words, once the photographic lens 2 is turned by 40.5° along thecounterclockwise direction from the correct interlock phase, theaccessory mount 200 becomes engaged with the body mount 100 (engagementof the accessory-side tabs and the body-side tabs is completed) andthus, the photographic lens 2 becomes fully mounted. The rotationalangle of 40.5°, by which the photographic lens 2 is turned from thecorrect interlock phase to the phase at which mounting of thephotographic lens 2 is completed, is to be referred to as a mountingangle. In addition, the counterclockwise turning direction mentionedabove may be otherwise referred to as a mounting direction.

When the photographic lens 2 is fully mounted, the position of the pinhole 261 at the accessory mount 200 is aligned with the position of thepin hole 161 at the body mount 100. The pin (not shown) projecting outthrough the pin hole 161 at the body mount 100 is thus inserted throughthe pin hole 261.

—Dismounting the Photographic Lens 2 from the Camera Body 1—

The photographic lens 2 is dismounted from the camera body 1 through thefollowing procedure. A button (not shown) disposed at the camera body 1is depressed so as to retract the pin mentioned above from the pin hole261. As the photographic lens 2 is turned back to the correct interlockphase along the clockwise direction viewed from the front side of thecamera body 1 in this state, the accessory-side tabs and the body-sidetabs become dismounted. When the photographic lens 2 is turned to thecorrect interlock phase, the restricting member 262 comes in contactwith the first side end 111 of the body-side first tab 110, therebypreventing further rotation along the clockwise direction. In otherwords, the state shown in FIG. 7 is resumed. Since the body-side tabs110 to 130 and the accessory-side tabs 210 to 230 do not interfere witheach other at the correct interlock position, as explained earlier, thephotographic lens 2 can be pulled forward and separated from the camerabody 1. It is to be noted that the clockwise turning direction mentionedabove may be otherwise referred to as a dismounting direction.

—State of Engagement Between Accessory-Side Tabs and Body-Side Tabs—

FIG. 9 is a schematic view of the body-side first tab 110 expanded alongthe circumferential direction, taken from the outer circumferential sideof the photographic lens 2. The body-side first tab 110 includes atapered surface 117 formed on the side where the rear surface 114 islocated, near the second side end 112. The tapered surface 117 is formedso as to allow the accessory-side first tab 210 to smoothly move into aposition to the rear of the body-side first tab 110 while thephotographic lens 2 is being mounted. A contact portion 115, constitutedwith a surface ranging perpendicular to the direction extending fromfront to rear relative to the body mount 100, is formed continuous tothe tapered surface 117 at the body-side first tab 110 near the secondside end 112. At the rear surface 114, a spring 116 is disposed at aposition adjacent to the contact portion 115.

The spring 116 is an elastic member that comes in contact with the frontsurface 214 (not shown in FIG. 9) of the accessory-side first tab 210having moved into the position to the rear of the body-side first tab110 and presses the front surface 214 rearward. With the spring 116, astate in which the accessory mount reference surface 201 and the bodymount reference surface 101 remain in contact with each other issustained. If an external force that would cause the photographic lens 2to tilt relative to the camera body 1 against the force applied by thespring 116 is applied to the photographic lens 2 having become fullymounted, the contact portion 115 comes in contact with the front surface214 of the accessory-side first tab 210 to restrict any forwarddisplacement of the accessory-side first tab 210. It is to be notedwhile the force applied by the spring 116 keeps the accessory mountreference surface 201 and the body mount reference surface 101 incontact (tight contact) with each other, the contact portion 115 is setslightly apart from the front surface 214 of the accessory-side firsttab 210.

The body-side second tab 120 and the body-side third tab 130 adoptstructures similar to that described above. Namely, the body-side secondtab 120 includes a tapered surface 127 formed on the side where the rearsurface 124 is located, near the second side end 122. A contact portion125, constituted with a surface ranging perpendicular to the directionextending from front to rear relative to the body mount 100, is formedcontinuous to the tapered surface 127 at the body-side second tab 120near the second side end 122. At the rear surface 124, a spring 126 isdisposed at a position adjacent to the contact portion 125. Thebody-side third tab 130 includes a tapered surface 137 formed on theside where the rear surface 134 is located, near the second side end132. A contact portion 135, constituted with a surface rangingperpendicular to the direction extending from front to rear relative tothe body mount 100, is formed continuous to the tapered surface 137 atthe body-side third tab 130 near the second side end 132. At the rearsurface 134, a spring 136 is disposed at a position adjacent to thecontact portion 135.

A mark assigned with reference numeral 116 a in FIG. 8 indicates theposition at which the spring 116 presses the front surface 214 of theaccessory-side first tab 210, i.e., the specific phase of the springforce pressing position assumed along the circumferential direction.Likewise, a mark assigned with reference numeral 126 a indicates thespecific phase of the position at which the spring 126 presses the frontsurface 224 of the accessory-side second tab 220 assumed along thecircumferential direction, and a mark assigned with reference numeral136 a indicates the specific phase of the position at which the spring136 presses the front surface 234 of the accessory-side third tab 230assumed along the circumferential direction.

As indicated in FIGS. 7 and 8, the contact portion 115 is locatedsubstantially at the top center of the body mount 100. The contactportion 125 is disposed at a position set apart from the second side end122 of the body-side second tab 120 by a distance equal to the distancesetting the contact portion 115 apart from the second side end 112 atthe body-side first tab 110. The contact portion 135 is disposed at aposition set apart from the second side end 132 of the body-side thirdtab 130 by a distance equal to the distance setting the contact portion115 apart from the second side end 112 at the body-side first tab 110.

FIGS. 10A through 10F show changes in the state of engagement betweenthe accessory-side second tab 220 and the body-side second tab 120occurring in time series as the photographic lens 2 is mounted at thecamera body 1 and then is dismounted from the camera body 1 in schematicviews of the body-side second tab 120 expanded along the circumferentialdirection, taken from the outer side along the radial direction. FIG.10A shows the accessory-side second tab 220 of the accessory mount 200having been inserted at the correct interlock phase, passing through thebody-side second gap 152. FIG. 10B shows the state of the accessory-sidesecond tab 220 and the body-side second tab 120 assumed after theaccessory-side second tab 220 passes through the body-side second gap152 and the accessory mount reference surface 201 comes into contactwith the body mount reference surface 101.

Subsequently, the photographic lens 2 is turned along the mountingdirection, causing the accessory-side second tab 220 to move into aposition to the rear of the body-side second tab 120, as shown in FIG.10C. The accessory-side second tab 220 further moves to the rear of thespring 126, resulting in an application of a rearward force by thespring 126 to the accessory-side second tab 220, as illustrated in FIG.10D. Once the photographic lens 2 is turned from the correct interlockphase by an extent matching the mounting angle along the mountingdirection, the restricting member 262 comes into contact with the secondside end 122 of the body-side second tab 120, as shown in FIG. 10E,thereby preventing further rotation of the photographic lens 2 along themounting direction.

In the state shown in FIG. 10E, the photographic lens 2 is turned alongthe dismounting direction in order to dismount the photographic lens 2from the camera body 1. Once the photographic lens 2 is turned along thedismounting direction by an extent matching the mounting angle, therestricting member 262 comes in contact with the first side end 111 ofthe body-side first tab 110, as illustrated in FIG. 10F, therebypreventing further rotation of the photographic lens 2 along thedismounting direction.

—Insertion of the Photographic Lens 2 at a Phase Other than the CorrectInterlock Phase—

If the user attempts to insert the photographic lens 2 at a phase otherthan the correct interlock phase, at least two tabs among the body-sidetabs 110 to 130 and at least two tabs among the accessory-side tabs 210to 230 come into contact with each other at, at least, two locations,and thus, insertion of the accessory mount 200 through the body mount100 is disallowed (deterred) in the embodiment.

As can be surmised by viewing FIG. 7, if the user attempts to mount thephotographic lens 2 slightly offset from the correct interlock phasealong the counterclockwise direction in the figure, the rear surface 213of the accessory-side first tab 210 will come into contact with thefront surface 113 of the body-side first tab 110, the rear surface 223of the accessory-side second tab 220 will come into contact with thefront surface 123 of the body-side second tab 120, and the rear surface233 of the accessory-side third tab 230 will come into contact with thefront surface 133 of the body-side third tab 130. As a result, the threebody-side tabs 110 to 130 and the three accessory-side tabs 210 to 230will be in contact with each other and insertion of the accessory mount200 into the body mount 100 will be disallowed. This situation may arisewhen, for instance, the accessory-side tabs 210 to 230 in FIG. 8 arepositioned frontward relative to the body-side tabs 110 to 130.

If the user attempts to mount the photographic lens 2 turned by agreater extent along the counterclockwise direction relative to thestate described above, the accessory-side second tab 220 will movefrontward relative to the body-side third gap 153, as shown in FIG. 11and thus, the accessory-side second tab 220 will no longer be in contactwith any of the body-side tabs 110 to 130. However, the rear surface 213of the accessory-side first tab 210 will be contact with the frontsurface 113 of the body-side first tab 110 and the rear surface 233 ofthe accessory-side third tab 230 will be contact with the front surface133 of the body-side third tab 130. In this situation, the contactachieved by the two body-side tabs among the body-side tabs 110 to 130and the two accessory-side tabs among the accessory-side tabs 210 to 230disallows insertion of the accessory mount 200 through the body mount100. The contact thus achieved by the body-side tabs 110 to 130 and theaccessory-side tabs at a total of two contact locations, is indicated asthe hatched areas in FIG. 11.

A slight counterclockwise rotation of the photographic lens 2 will alterthe positional relationship of the two mounts relative to each other inFIG. 11 to a positional relationship whereby the rear surface 213 of theaccessory-side first tab 210 contacts the front surface 123 of thebody-side second tab 120. Namely, a slight counterclockwise turn of thephotographic lens 2 will allow the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 to achieve contact at three contactlocations. If, on the other hand, the photographic lens 2 in the stateshown in FIG. 11 is turned along the clockwise direction, the rearsurface 213 of the accessory-side first tab 210 and the front surface113 of the body-side first tab 110 will contact each other over a largerarea and the rear surface 233 of the accessory-side third tab 230 andthe front surface 133 of the body-side third tab 130 will contact eachother over a larger area.

In other words, FIG. 11 shows a state in which the contact of the rearsurface 213 of the accessory-side first tab 210 and the front surface113 of the body-side first tab 110 and the contact of the rear surface233 of the accessory-side third tab 230 and the front surface 133 of thebody-side third tab 130 are achieved at the two contact locations overthe smallest contact area. The rear surface 213 of the accessory-sidefirst tab 210 and the front surface 113 of the body-side first tab 110contact each other at the interlock phase shown in FIG. 11 over anangular range, assumed by viewing the body mount 100 from the front sideof the camera body 1, of 11°.

It is to be noted that there are other situations in which insertion ofthe accessory mount 200 through the body mount 100 is disallowed via atotal of two contact locations where two tabs among the body-side tabs110 to 130 and two tabs among the accessory-side tabs 210 to 230 contacteach other, as described in detail later. Among the plurality of statesin which insertion of the accessory mount 200 through the body mount 100is disallowed via a total of two contact locations where two tabs amongthe body-side tabs 110 to 130 and two tabs among the accessory-side tabs210 to 230 achieve contact, the smallest contact area is formed ateither of the two contact locations is the in two specific conditions,i.e., the state shown in FIG. 11 and the state (not shown) achieved byrotating the photographic lens 2 in the state shown in FIG. 11 by 11°along the counterclockwise direction in the figure, as described below.

If the photographic lens 2 with the two mounts assuming the specificpositional relationship relative to each other as shown in FIG. 11 isturned by 11° along the counterclockwise direction in the figure, thecontact of the rear surface 213 of the accessory-side first tab 210 andthe front surface 113 of the body-side first tab 110 will cease but therear surface 213 of the accessory-side first tab 210 will come intocontact with the front surface 123 of the body-side second tab 120. Itis to be noted that contact will also be achieved as the rear surface233 of the accessory-side third tab 230 comes into contact with thefront surface 133 of the body-side third tab 130. The rear surface 213of the accessory-side first tab 210 and the front surface 123 of thebody-side second tab 120 will contact each other over an angular range,assumed by viewing the body mount 100 from the front side of the camerabody 1, of 11°, as in the state shown in FIG. 11.

Thus, in this case too, contact will be achieved by the body-side tabs110 to 130 sand the accessory-side tabs 210 to 230 at a total of twocontact locations. Among various states in which contact is achieved bythe rear surface 213 of the accessory-side first tab 210 and the frontsurface 123 of the body-side second tab 120 and contact is achieved bythe rear surface 233 of the accessory-side third tab 230 and the frontsurface 133 of the body-side third tab 130 at a total of two contactlocations, the accessory-side tabs and the body-side tabs contact eachother over the smallest area in this state.

Namely, while there are various insertion disallowed states, in whichinsertion of the accessory mount 200 through the body mount 100 isdisallowed via a total of two contact locations where two tabs among thebody-side tabs 110 to 130 and two tabs among the accessory-side tabs 210to 230 contact each other, the rear surface 213 the accessory-side firsttab 210 and the front surface 113 of the body-side first tab 110 contacteach other over the smallest contact area in the state shown in FIG. 11.Likewise, the smallest contact area is also formed by the rear surface213 of the accessory-side first tab 210 and the front surface 123 of thebody-side second tab 120 in the insertion disallowed state with thephotographic lens 2 turned counterclockwise by 11° relative to the stateshown in FIG. 11, among the insertion disallowed states in whichinsertion of the accessory mount 200 through the body mount 100 isdisallowed via a total of two contact locations where two tabs among thebody-side tabs 110 to 130 and 2 tabs among the accessory-side tabs 210to 230 contact each other. The interlock phase shown in FIG. 11 and theinterlock phase assumed with the photographic lens 2 turned by 11° alongthe counterclockwise direction relative to the state shown in FIG. 11are each referred to as a specific interlock phase.

As described above, a counterclockwise rotation of the photographic lens2 in the state shown in FIG. 11 will cause the rear surface 213 of theaccessory-side first tab 210 to come into contact with both the frontsurface 113 of the body-side first tab 110 and the front surface 123 ofthe body-side second tab 120 and cause the rear surface 233 of theaccessory-side third tab 230 to come into contact with the front surface133 of the body-side third tab 130. In other words, the body-side tabs110 to 130 and the accessory-side tabs 210 to 230 will achieve contactat a total of three contact locations.

As the photographic lens 2 is turned further counterclockwise in thefigure until the photographic lens 2 is rotated by 11° along thecounterclockwise direction relative to the state shown in FIG. 11, asdescribed above, the rear surface 213 of the accessory-side first tab210 and the front surface 113 of the body-side first tab 110 will ceaseto be in contact with each other and thus, the number of contactlocations where the body-side tabs 110 to 130 and the accessory-sidetabs 210 to 230 contact each other will be reduced to two.

As the photographic lens 2 is turned further along the counterclockwisedirection in the figure, the state shown in FIG. 12 will be achieved.

As can be surmised by viewing FIG. 12, a slight counterclockwise turn ofthe photographic lens 2 will alter the positional relationship shown inFIG. 12, causing the rear surface 223 of the accessory-side second tab220 to come into contact with the front surface 133 of the body-sidethird tab 130. In other words, contact will be achieved by the body-sidetabs 110 to 130 and the accessory-side tabs 210 to 230 at a total ofthree contact locations. A further counterclockwise turn of thephotographic lens 2 will cause the rear surface 233 of theaccessory-side third tab 230 to come into contact with the front surface113 of the body-side first tab 110 as well. In this situation, contactwill be achieved by the body-side tabs 110 to 130 and the accessory-sidetabs 210 to 230 over a total of four contact locations.

As the photographic lens 2 is turned further counterclockwise, the rearsurface 233 of the accessory-side third tab 230 and the front surface133 of the body-side third tab 130 will cease contact with each otherand then, the rear surface 213 of the accessory-side first tab 210 andthe front surface 123 of the body-side second tab 120, too, will ceasecontact with each other. In other words, contact will be achieved by thebody-side tabs 110 to 130 and the accessory-side tabs 210 to 230 at atotal of two contact locations under these circumstances, as shown inFIG. 13.

A further counterclockwise turn of the photographic lens 2 in the stateshown in FIG. 13 will cause a decrease in both the contact area overwhich the rear surface 223 of the accessory-side second tab 220 and thefront surface 133 of the body-side third tab 130 are in contact witheach other and the contact area over which the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 are contact with each other. In other words, FIG. 13 showsa state in which the contact of the rear surface 223 of theaccessory-side second tab 220 and the front surface 133 of the body-sidethird tab 130 and the contact of the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 are achieved at the two contact locations over the largestcontact area.

FIG. 14 shows a state achieved by further turning the photographic lens2 along the counterclockwise direction relative to the state shown inFIG. 13. Among various states in which the rear surface 223 of theaccessory-side second tab 220 and the front surface 133 of the body-sidethird tab 130 contact each other and the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 contact each other at a total of two contact locations,the accessory-side tabs and the body-side tabs contact each other overthe smallest area in this state.

A slight counterclockwise turn of the photographic lens 2 relative tothe state shown in FIG. 14 will allow the rear surface 213 of theaccessory-side first tab 210 and the front surface 133 of the body-sidethird tab 130 to come into contact with each other. At this time,contact will be achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of three contact locations. Asthe photographic lens 2 in this state is turned further along thecounterclockwise direction in the figure, the rear surface 233 of theaccessory-side third tab 230 and the front surface 123 of the body-sidesecond tab 120 will come into contact with each other. In this state,contact will be achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of four contact locations. Asthe photographic lens 2 in this state is turned further along thecounterclockwise direction in the figure, the rear surface 223 of theaccessory-side second tab 220 and the front surface 133 of the body-sidethird tab 130 will cease contact with each other, as shown in FIG. 15.At this time, contact will be achieved by the body-side tabs 110 to 130and the accessory-side tabs 210 to 230 at a total of three contactlocations.

As the photographic lens 2 is slightly turned along the counterclockwisedirection relative to the state shown in FIG. 15, the rear surface 223of the accessory-side second tab 220 and the front surface 113 of thebody-side first tab 110 will come into contact with each other butsubstantially simultaneously, the contact of the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 will cease. As the photographic lens 2 is turned furtheralong the counterclockwise direction in the figure, the correctinterlock phase shown in FIG. 7 will be reestablished and any contact(interference) between the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 will cease.

—Accessory-Side Third Tab 230—

When contact is achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of two contact locations withthe accessory-side third tab 230 in contact with a body-side tab at oneof the contact locations, the accessory-side third tab 230 invariablycontacts the body-side tab 110, 120 or 130 on the side where its secondside end 232 is located (i.e., at the rear surface 233 near the secondside end 232), rather than on the side where its first side end 231 islocated (i.e., at the rear surface 233 near the first side end 231), asshown in FIGS. 11 through 14. In other words, when contact is achievedby the body-side tabs 110 to 130 and the accessory-side tabs 210 to 230at a total of two contact locations and the accessory-side third tab 230achieves contact at one of the contact locations, the function ofpreventing erroneous insertion is achieved in the area near the secondside end 232 of the accessory-side third tab 230. The accessory-sidethird tab 230 is formed so that the area near its second side end 232 ispositioned in the body-side third gap 153 without overlapping thebody-side third tab 130 when the photographic lens 2 is mounted at thecamera body 1 as shown in FIG. 8. Namely, when the photographic lens 2is mounted at the camera body 1, the area near the second side end 232of the accessory-side third tab 230 does not directly contribute tolocking of the photographic lens 2 to the camera body 1.

In addition, near the first side end 231 of the accessory-side third tab230, the front surface 234 is pressed by the spring 136 at the body-sidethird tab 130, and whenever an excessive external force is applied, thefront surface 234 will come into contact with the contact portion 135,as explained earlier. This means that when the photographic lens 2 ismounted at the camera body 1, the force applied to lock the photographiclens 2 to the camera body 1 will be imparted primarily to the area nearthe first side end 231 at the accessory-side third tab 230.

In summary, the accessory-side third tab 230 is formed so that differentfunctions are achieved in the area near the first side end 231 and thearea near the second side end 232 along the direction in which theaccessory-side third tab 230 extends.

—Body-Side First Tab 110—

When contact is achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of two contact locations withthe body-side first tab 110 in contact with an accessory-side tab at oneof the contact locations, the body-side first tab 110 invariablycontacts the accessory-side tab 210, 220 or 230 on the side where itsfirst side end 111 is located (i.e., at the front surface 113 near thefirst side end 111), rather than on the side where its second side end112 is located (i.e., at the front surface 113 near the second side end112), as shown in FIGS. 11, 13 and 14. In other words, when contact isachieved by the body-side tabs 110 to 130 and the accessory-side tabs210 to 230 at a total of two contact locations and the body-side firsttab 110 achieves contact at one of the contact locations, the functionof preventing erroneous insertion is achieved in the area near the firstside end 111 of the body-side first tab 110.

The spring 116 is disposed adjacent to the contact portion 115 at thebody-side first tab 110 over the area near its second side end 112.Namely, the function of locking the photographic lens 2 having beenmounted at the camera body 1 is achieved over the area near the secondside end 112 of the body-side first tab 110.

In summary, the body-side first tab 110 is formed so that differentfunctions are achieved in the area near the first side end 111 and thearea near the second side end 112 along the direction in which thebody-side first tab 110 extends.

The camera body 1 and the photographic lens 2 structured as describedabove achieve the following advantages.

(1) Three accessory-side tabs 210 to 230 assuming a uniform size anddisposed over equal intervals and three body-side tabs 110 to 130assuming a uniform size and disposed over equal intervals will allow thephotographic lens 2 to be mounted at the camera body 1 at a phase otherthan the correct interlock phase. Accordingly, the three accessory-sidetabs 210 to 230 are formed in varying sizes and are disposed overvarying intervals and the three body-side tabs 110 to 130 are alsoformed in varying sizes and disposed over varying intervals. Inaddition, even if the user attempts to insert the photographic lens 2 ata phase other than the correct interlock phase, at least two tabs amongthe body-side tabs 110 to 130 and at least two tabs among theaccessory-side tabs 210 to 230 come into contact with each other at atotal of at least two contact locations, so as to disallow insertion ofthe accessory mount 200 through the body mount 100. If contact wasachieved by a camera accessory mount tab and a camera body mount tab ata single contact location, the other two contact-free tabs on theaccessory-side could assume positions between camera body-side tabs. Incontrast, contact is achieved in the embodiment by the body-side tabs110 to 130 and the accessory-side tabs 210 to 230 at, at least, twocontact locations at a phase other than the correct interlock phase asdescribed above, and consequently, erroneous mounting of the cameraaccessory can be reliably prevented.

(2) The restricting member 262, which comes in contact with the secondside end 122 of the body-side second tab 120 and the first side end 111of the body-side first tab 110, restricts the range over which thephotographic lens 2 can be turned along the mounting direction and thedismounting direction. Since the rotational range of the photographiclens 2 along the mounting direction and the dismounting direction can berestricted via a single member assuming a simple shape, themanufacturing costs of the body mount 100 and the accessory mount 200can be minimized.

(3) The restricting member 262 is disposed near a side end of theaccessory-side second tab 220 assuming a smallest length along thecircumference of the accessory mount 200. At the correct interlockphase, the accessory-side second tab 220 passes through the body-sidesecond gap 152, which extends over an angular range of 47.5° along thecircumferential edge of the circular opening of the camera body 1. Inaddition, the mounting angle assumed in the embodiment is 40.5°. Thismeans that a range, over which the restricting member 262 is allowed tomove between the second side end 122 of the body-side second tab 120 andthe first side end 111 of the body-side first tab 110 within the angularrange (47.5° of the body-side second gap 152, is equivalent to themounting angle. Accordingly, by disposing the restricting member 262near a side end of the accessory-side second tab 220 assuming thesmallest length along the circumference of the accessory mount 200, themounting angle for the mount system constituted with the body mount 100and the accessory mount 200 is defined. From a different perspective,the mounting angle setting can be rationalized as described below andthe sizes of the body-side second gap 152 and the accessory-side secondtab 220 may be regarded to have been set in correspondence to themounting angle rationalized as described below. In any case, thesestructural features achieve a rational overall structure with nosuperfluous structural elements, to contribute toward minimization ofthe overall weight.

It is to be noted that at a smaller mounting angle, the accessory can beengaged with greater ease, the extent to which electrical contact points(not shown) at the camera body 1 and at the photographic lens 2 slideagainst each other can be reduced and the extent of wear of theelectrical contact points occurring whenever the photographic lens 2 isexchanged can be reduced. However, if the mounting angle is very small,tabs engaged with each other may become inadvertently dismounted fromeach other, and in such a case, the photographic lens 2 may fall fromthe camera body. At the same time, the body mount 100 must assume acertain circumferential dimension in order to accommodate the springs116, 126 and 136, the contact portions 115, 125 and 135 and the taperedsurfaces 117, 127 and 137. Moreover, a sufficient mounting angle isrequired to ensure that the accessory-side tabs 210 to 230 are allowedto reliably mount the springs 116, 126 and 136 and the contact portions115, 125 and 135 over the tapered surfaces 117, 127 and 137. Themounting angle of 40.5° adopted in the embodiment has been determined bytaking into consideration all these factors.

(4) While the weight distribution of the photographic lens 2 is suchthat the photographic lens 2 tends to pull down on its front side(subject side), the forces applied from the springs 116, 126 and 136sustain the accessory mount reference surface 201 in contact with thebody mount reference surface 101 under typical operating conditions.However, if an external force exceeding the force of the springs,working along a direction matching that of gravity is applied to thephotographic lens 2 in a photographing state with the camera body 1 inthe upright attitude fixed to, for instance, a tripod, the spring 116 ofthe uppermost body-side first tab 110 will flex further to allow thefront surface 214 of the accessory-side first tab 210 to come in contactwith the contact portion 115 of the body-side first tab 110.

FIG. 16 illustrates this condition. It is to be noted that the intervalsand the like formed between the individual parts are exaggerated in FIG.16 so as to provide a clear illustration. In the state shown in FIG. 16,the accessory mount reference surface 201 and the body mount referencesurface 101 are in contact with each other at a point PD on the lowerside, the front surface 214 of the accessory-side first tab 210 and thecontact portion 115 of the body-side first tab 110 are in contact witheach other at a point PU on the upper side as described above and theweight of the photographic lens 2 and the external force applied to thephotographic lens 2 are supported at these two points. Accordingly, theforce applied to the two points PD and PU can be reduced by maximizingthe distance LS extending along the vertical direction (along thedirection of gravitational force) between the two points PD and PU.

This situation will not arise in a normal photographing condition unlessan unintended external force is applied. However, the photographic lens2, which normally assumes a cylindrical shape, tends to come intocontact with various objects in real-world usage and may be employed ina range of circumstances. For this reason, the condition shown in FIG.16 may be expected to arise fairly often and, therefore it is importantto devise measures to effectively address the issues arising from suchcircumstances.

FIGS. 17 through 19 each indicate the contact points PD and PU and thedistance LS corresponding to a specific attitude assumed by the camerabody 1. It is to be noted that the camera body 1 assumes the uprightattitude (lateral orientation) in FIG. 17, with the distance LS and thecontact points PD and PU corresponding to this attitude respectivelynotated as LS1, PD1 and PU1. The camera body 1 assumes a longitudinalorientation in FIG. 18 achieved by turning the left side of the camerabody 1 upward, with the distance LS and the contact points PD and PUcorresponding to this attitude respectively notated as LS2, PD2 and PU2.The camera body 1 assumes a longitudinal orientation in FIG. 19 achievedby turning the right side of the camera body 1 upward, with the distanceLS and the contact points PD and PU corresponding to the particularattitude respectively notated as LS3, PD3 and PU3. The distance LS1assumed in the lateral orientation in FIG. 17 and the distance LS2assumed in the longitudinal orientation in FIG. 18 are bothsubstantially equal to the diameter of the body mount 100. However, thedistance LS3 in the longitudinal orientation shown in FIG. 19 ismarkedly smaller than the distances LS1 and LS2.

For this reason, at a given level of external force applied to thephotographic lens 2, the level of force working at PU3 will be greaterthan the levels of force working at PU1 and PU2.

Accordingly, the body-side third tab 130 in the embodiment is formed soas to assume a greater length along the circumferential directioncompared to the body-side first tab 110 and the body-side second tab120. Greater strength is thus assured for the body-side third tab 130over the body-side first tab 110 and the body-side second tab 120. Inaddition, the accessory-side third tab 230 at the accessory mount 200,which is to come into contact with the contact portion 135 (i.e., PU3)when the photographic lens 2 is fully mounted, is formed to achieve agreater length along the circumferential direction than theaccessory-side first tab 210 and the accessory-side second tab 220.Consequently, since ample strength is assured at the body-side third tab130 and the accessory-side third tab 230, the body-side third tab 130and the accessory-side third tab 230, which are to be subjected to thehighest levels of force, will remain intact even when the camera body 1assumes the longitudinal orientation shown in FIG. 19.

As described above, the advantage of reliably disallowing erroneousinsertion at a phase other than the correct interlock phase and theadvantage of assuring sufficient strength for the accessory mount 200and the body mount 100 when the photographic lens 2 having been insertedat the correct interlock phase is fully mounted can both be achievedthrough the embodiment described above.

(5) As explained earlier, different functions are achieved in the areanear the first side end 231 and in the area near the second side end 232along the direction in which the accessory-side third tab 230 extends.As a result, the durability of the accessory-side third tab 230 isimproved. The accessory-side third tab 230, where the application offorce at PU3 occurs when the camera body 1 assumes the longitudinalorientation with the right side thereof turned upward, is subjected tothe highest level of force. With the durability of this accessory-sidethird tab 230 coming under the heaviest onus improved as describedabove, the durability and the reliability of the accessory mount 200itself are improved.

(6) As explained earlier, different functions are achieved in the areanear the first side end 111 and in the area near the second side end 112along the direction in which the body-side first tab 110 extends. Thedurability of the body-side first tab 110 is thus improved. Thebody-side first tab 110, where the spring 116, which, under the weightof the photographic lens 2, is subjected to a more significant andcontinuous onus compared to the other springs 126 and 136, and theapplication of force occurs at Pu1 as described earlier when the camerabody 1 assumes the typical lateral orientation, is subjected to an onusmost frequently. Since the durability of the body-side first tab 110coming under the most frequent onus is improved, the durability and thereliability of the body mount 100 itself are improved.

(7) The contact portion 115 is set substantially at the top center ofthe body mount 100 in the structure achieved in the embodiment and thus,a large value can be set for LS1 mentioned earlier. As a result, thelevel of force applied at the contact point PU1 can be reduced, whichimproves the durability of the body-side first tab 110 and effectivelyprevents the photographic lens 2 from drooping down at its front side.At the same time, the body-side first tab 110 is set at the top centerof the body mount 100 and, as a result, sufficient strength is assuredfor the contact portion 115. As a result, the durability of thebody-side first tab 110 is improved. This ultimately leads toimprovements both in the durability and in the reliability of the bodymount 100.

(8) As indicated in FIG. 16, the lower areas of the rear surfaces of thebody-side tabs 110 to 130 and the lower areas of the front surfaces ofthe accessory-side tabs 210 to 230 come into contact with each otherleast readily. This means that there is not a significant need forhaving the body-side tabs 110 to 130 and the accessory-side tabs 210 to230 come into contact with each other over these areas. Accordingly, thelargest body-side third gap 153 in the embodiment is positioned on thelower side of the body mount 100, as illustrated in FIG. 5. This, inturn, ensures that the body-side tabs 110 to 130 can be positioned in ahighly rational configuration.

(9) The following is the rationale for disposing the accessory-side tabs210 to 230 at the specific positions indicated in FIG. 6. Namely, it isdesirable to assure a high degree of strength with a greater lengthassumed along the circumferential direction at the accessory-side firsttab 210, which is positioned at the top center when the photographiclens 2 is mounted at the camera body 1 assuming the lateral orientation.However, since the largest body-side third gap 153 is set on the lowerside of the body mount 100, as described earlier, the accessory-sidethird tab 230, which passes through the body-side third gap 153 when theaccessory mount is inserted at the correct interlock phase, is formed torange over the greatest length along the circumferential direction.Accordingly, the accessory-side first tab 210 is formed to range over asecond largest length along the circumferential direction. Theaccessory-side second tab 220, which is not subjected to as manyrequirements, is formed so as to extend over a smallest range along thecircumferential direction. The accessory-side tabs 210 to 230 formed asdescribed above can be disposed with a high level of rationality.

Second Embodiment

In reference to FIGS. 23 through 36, the camera accessory, the accessorymount, the camera body and the camera body mount achieved in a secondembodiment of the present invention are described. FIG. 23 is aschematic perspective of a camera body 1 with the exchangeable lensesand an exchangeable photographic lens 2 that may be detachably mountedat the camera body 1, achieved in the second embodiment. A shutterrelease button 4, an image sensor 5 and a control circuit 6 thatcontrols various units of the camera body 1 are disposed at the camerabody 1. Reference numeral 3 indicates a photographic optical paththrough which a subject image departing the photographic lens 2 isguided to the image sensor 5. Reference numeral 9 indicates a lensretainer lock pin used to lock the photographic lens 2 having beenmounted fully at the camera body 1, so as to disallow rotation thereof.

—Body-Mount 100—

FIG. 24A is a schematic perspective illustrating the structure of thebody mount 100, viewed along a diagonal direction from a front rightviewpoint relative to the camera body 1 and FIG. 24B is a sectional viewof the body mount 100 over an area around the lens retainer lock pin 9.The body mount 100 adopts a bayonet structure that includes three tabs(body-side tabs) set apart from one another along the circumferentialedge of a circular opening (photographic optical path) at the camerabody 1, each projecting inward from the outer side of the openingcircumference. Among the three body-side tabs, the body-side tab locatedat the uppermost position is referred to as a body-side first tab 110,the body-side tab located next to the body-side first tab 110 along thecounterclockwise direction in the figure is referred to as a body-sidesecond tab 120 and the body-side tab located next to the body-sidesecond tab 120 along the counterclockwise direction is referred to as abody-side third tab 130.

Reference numeral 101 indicates a body mount reference surface. The bodymount reference surface 101 is a ring-shaped flat surface formed so asto face toward the front side. As the photographic lens 2 is mounted atthe camera body 1, the body mount reference surface 101 comes intocontact with an accessory mount reference surface 201 of the accessorymount 200, which is to be described in detail later, thereby regulatingthe position assumed by the photographic lens 2 along the front-reardirection. Reference numeral 102 indicates an inner circumferentialsurface of the cylindrical body mount 100. The inner circumferentialsurface 102, which interlocks with a fitting portion 202 of theaccessory mount 200 to be detailed below, is used as a referencesurface, in reference to which the optical axis of the photographic lens2 is aligned with the optical axis of the camera body 1 (the centralaxis of the photographic optical path 3). Reference numeral 161indicates a pin hole through which the lens retainer lock pin 9 projectsout or retracts in. It is to be noted that a force applied by a spring(not shown) pushes the lens retainer lock pin 9 to project out at thebody mount reference surface 101, as shown in FIG. 24 B. As the userpresses a lens release button (not shown), the lens retainer lock pin 9retracts backward relative to the body mount reference surface 101against the force imparted by the spring (not shown).

—Accessory Mount 200—

FIG. 25 is a perspective schematically illustrating the structure of theaccessory mount 200, viewed along a diagonal direction from a rear leftviewpoint relative to the photographic lens 2. It is to be noted thatFIG. 25 shows the accessory mount 200 with the photographic lens 2 fullymounted at the camera body 1 (mounting complete state), i.e., in aphotographing-enabled state. This means that the top-bottom/left-rightorientation of the accessory mount 200 shown in FIG. 25 matches thetop-bottom/left-right orientation of the camera body 1. Unlessspecifically noted, the following description is given by assuming thatthe top-bottom/left-right orientation of the accessory mount 200 is theorientation in the mounting complete state.

The accessory mount 200 adopts a bayonet structure that includes threetabs (accessory-side tabs) set apart from one another along thecircumferential direction, each projecting from the inner side of thecircumference toward the outer side of the circumference. Among thethree accessory-side tabs, the accessory-side tab located at theuppermost position is referred to as an accessory-side first tab 210,the accessory-side tab located next to the accessory-side first tab 210along the clockwise direction in the figure is referred to as anaccessory-side second tab 220 and the accessory-side tab located next tothe accessory-side second tab 220 along the clockwise direction isreferred to as an accessory-side third tab 230.

The space created between two consecutive accessory-side tabs throughwhich a body-side tabs passes when the photographic lens 2 is beingmounted or dismounted as explained later, is referred to as anaccessory-side gap. The accessory-side gap present between theaccessory-side first tab 210 and the accessory-side second tab 220 isreferred to as an accessory-side first gap 251, the accessory-side gaplocated next to the accessory-side first gap 251 along the clockwisedirection in the figure is referred to as an accessory-side second gap252 and the accessory-side gap located next to the accessory-side secondgap along the clockwise direction is referred to as an accessory-sidethird gap 253.

The surface of the accessory-side first tab 210 facing rearward isreferred to as a rear surface 213, the side end of the accessory-sidefirst tab 210 facing the accessory-side first gap 251 is referred to asa first side end 211 and the side end of the accessory-side first tab210 facing the accessory-side third gap 253 is referred to as a secondside end 212. Likewise, the surface of the accessory-side second tab 220facing rearward is referred to as a rear surface 223, the side end ofthe accessory-side second tab 220 facing the accessory-side second gap252 is referred to as a first side end 221, and the side end of theaccessory-side second tab 220 facing the accessory-side first gap 251 isreferred to as a second side end 222. The surface of the accessory-sidethird tab 230 facing rearward is referred to as a rear surface 233, theside end of the accessory-side third tab 230 facing the accessory-sidethird gap 253 is referred to as a first side end 231 and the side end ofthe accessory-side third tab 230 facing the accessory-side second gap252 is referred to as a second side end 232. The first side ends 211,221 and 231 are tab ends facing toward the mounting direction, to bedescribed in detail later, whereas the second side ends 212, 222 and 232are tab ends facing toward a direction (dismounting direction) oppositethe mounting direction.

It is to be noted that, although not shown in FIG. 25, the surface ofthe accessory-side first tab 210 facing forward is referred to as afront surface 214. Likewise, the surface of the body-side second tab 220facing forward and the surface of the accessory-side third tab 230facing forward are respectively referred to a front surface 224 and afront surface 234.

Reference numeral 201 indicates an accessory mount reference surface.The accessory mount reference surface 201 is a ring-shaped flat surfaceformed so as to face rearward, and is in contact with the body mountreference surface 101 when the photographic lens 2 is fully mounted atthe camera body 1. Reference numeral 202 indicates a fitting portion.The fitting portion 202 is a cylindrical portion that fits at the innercircumferential surface 102 of the body mount 100 and is used forreference when aligning the optical axis of the photographic lens 2 withthe optical axis of the camera body 1 (the central axis of thephotographic optical path 3). Reference numeral 261 indicates a pinhole. As the lens retainer lock pin 9, which projects out or retractsinto the pin hole 161 at the body mount 100, is inserted through the pinhole 261, rotation of the fully mounted photographic lens 2 relative tothe camera body 1 (body mount 100) becomes disallowed and thephotographic lens 2 thus becomes locked.

A restricting member 262, which limits the rotation range of thephotographic lens 2 (accessory mount 200) relative to the camera body 1(body mount 100) while the photographic lens 2 is mounted or dismounted,is disposed frontward relative to the accessory-side second tab 220 nearits second side end 222, as shown in FIG. 25 and in FIGS. 26A and 26B.The restriction of the rotation range achieved via the restrictingmember 262 will be described in detail later. The restricting member 262may be, for instance, a headed pin screwed in from the outer side of theaccessory mount 200 along the radial direction. It is to be noted thatFIG. 26A shows the accessory-side second tab 220 near the second sideend 222, viewed from the rear-side, whereas FIG. 26B shows theaccessory-side second tab 220 near the second side and 222, viewed fromthe left side.

—Positions of Body-Side Tabs and Body-Side Gaps—

FIG. 27 indicates the positions of the body-side tabs and body-side gapsat the body mount 100 viewed from the front side of the camera body 1. Areference angular position is taken along the three o'clock direction atthe body mount 100 viewed from the front side of the camera body 1 andvarious angles representing the positions at which the body-side tabsare disposed, are assumed along the counterclockwise direction relativeto the three o'clock direction. Namely, the body-side first tab 110extends over an angular range of 76° to 130°, the body-side second tab120 extends over an angular range of 177.5° to 226° and the body-sidethird tab 130 extends over an angular range of 304.5° to 15° (375°).

The sizes of the individual body-side tabs 110 to 130 can each beindicated by the corresponding angular range along the circumferentialedge of the circular opening at the body mount 100. Namely, thebody-side first tab 110 has a 54° angular range, the body-side secondtab 120 has a 48.5° angular range and the body-side third tab 130 has a70.5° angular range. Likewise, the sizes of the individual body-sidegaps 151 to 153 can each be indicated by the corresponding angular rangealong the circumferential edge of the circular opening at the camerabody 1. Namely, the body-side first gap 151 has a 61° angular range, thebody-side second gap 152 has a 47.5° angular range and the body-sidethird gap 153 has a 78.5° angular range. The body-side second gap 152(47.5°) is thus the smallest gap at the camera body mount 100.

Reference numeral 7 in FIG. 27 indicates an index mark at the camerabody 1. The index mark 7 is used as a reference mark when mounting thephotographic lens 2 at the camera body 1. The index mark 7 assumes a 90°angular position counterclockwise relative to the reference threeo'clock direction taken at the body mount 100 viewed from the front sideof the camera body.

—Positions of Accessory-Side Tabs and Accessory-Side Gaps—

FIG. 28 indicates the positions of the accessory-side tabs and theaccessory-side gaps at the accessory mount 200 viewed from the rear sideof the photographic lens 2. A reference angular position is taken alongthe nine o'clock direction at the accessory mount 200 viewed from therear side of the photographic lens 2 fully mounted at the camera body.Various angles, representing the positions at which the accessory-sidetabs are disposed, are assumed along the clockwise direction relative tothe nine o'clock direction. Namely, the accessory-side first tab 210extends over an angular range of 56.5° to 115°, the accessory-sidesecond tab 220 extends over an angular range of 172.5° to 214.5° and theaccessory-side third tab 230 extends over an angular range of 272° to343.5°.

The ranges over which the accessory-side tabs 210 to 230 extend alongthe circumference of the accessory mount 200 can each be indicated bythe corresponding angular range along the circumference of the accessorymount 200. Namely, the accessory-side first tab 210 has a 58.5° angularrange, the accessory-side second tab 220 has a 42° angular range and theaccessory-side third tab 230 has a 71.5° angular range. In other words,the angles indicating the ranges of the first through thirdaccessory-side tabs, each representing the range of a circular arcextending along the circumferential direction, are; 58.7° for theaccessory-side first tab 210, 42° for the accessory-side second tab 220and 71.5° for the accessory-side third tab 230. This means that thesmallest tab among the accessory-side tabs is the accessory-side secondtab 220 (42°).

Likewise, the sizes of the individual accessory-side gaps 251 to 253 caneach be indicated by the corresponding angular range along thecircumference of the accessory mount 200. Namely, the accessory-sidefirst gap 251 has a 57.5° angular range, the accessory-side second gap252 has a 57.5° angular range and the accessory-side third gap 253 has a73° angular range.

Reference numeral 8 in FIG. 28 indicates an index mark 8 at thephotographic lens 2. The index mark 8 is used as a reference mark whenmounting the photographic lens 2 at the camera body 1. The index mark 8assumes a 130.5° angular position clockwise relative to the referencenine o'clock direction taken at the accessory mount 200 viewed from therear side of the photographic lens 2 in the mounting complete state.This angle is equal to a value representing the sum of 90° and amounting angle of 40.5° to be described in detail later.

As explained earlier, the restricting member 262 is disposed frontwardrelative to the accessory-side second tab 220 near its second side end222. This means that the restricting member 262 is disposed near theaccessory-side second tab 220 extending over the shortest range alongthe circumference of the accessory mount 200 (with the smallest angularrange along the circumference of the accessory mount 200).

—Mounting the Photographic Lens 2 at the Camera Body 1—

The photographic lens 2 structured as described above is mounted at thecamera body 1 through the following procedure. It is to be noted thatthe rotational position assumed by the photographic lens 2 relative tothe camera body 1 when the axis extending along the front-rear directionthrough the center of the photographic optical path 3 of the camera body1 and the optical axis of the photographic lens 2 are aligned with eachother is to be hereafter referred to simply as an interlock phase. Whilesustaining the alignment of the axis extending along the front-reardirection through the center of the photographic optical path 3 at thecamera body 1 and the optical axis of the photographic lens 2, thephotographic lens 2 is mounted at the camera body 1 by aligning therotational position of the index mark at the photographic lens 2 withthe rotational position of the index mark at the camera body 1. When thetwo index marks are aligned, the photographic lens 2 and the camera body1 achieve a positional relation relative to each other in which thebody-side tabs 110 to 130 and the accessory-side tabs 210 to 230 do notinterfere with each other, as shown in FIG. 29, and the accessory mount200 can be thus inserted through the body mount 100 until the accessorymount reference surface 201 contacts the body mount reference surface101. The interlock phase assumed in this state is to be referred to as acorrect interlock phase. It is to be noted that in FIG. 29, showing aspecific state of interference (state of overlap) between the body-sidetabs 110 to 130 and the accessory-side tabs 210 to 230, theaccessory-side tabs are shown as fan-shaped members in a schematicrepresentation.

As the accessory mount 200 is inserted at the body mount 100 at thecorrect interlock phase, the accessory-side first tab 210 passes fromfront to back through the body-side first gap 151, the accessory-sidesecond tab 220 passes from front to back through the body-side secondgap 152 and the accessory-side third tab 230 passes from front to backthrough the body-side third gap 153. Likewise, the body-side first tab110 passes from back to front through the accessory-side first gap 251(no reference numeral appended in FIG. 29), the body-side second tab 120passes from back to front through the accessory-side second gap 252 (noreference numeral appended in FIG. 29) and the body-side third tab 130passes from back to front through the accessory-side third gap 253 (noreference numeral appended in FIG. 29) as the accessory mount 200 isinserted through the body mount 100 at the correct interlock phase.

As the photographic lens 2 is turned along the counterclockwisedirection viewed from the front side of the camera body 1 after theaccessory mount 200 is inserted through the body mount 100 at thecorrect interlock phase, the accessory-side first tab 210 takes up aposition to the rear of the body-side first tab 110, the accessory-sidesecond tab 220 takes up a position to the rear of the body-side secondtab 120 and the accessory-side third tab 230 takes up a position to therear of the body-side third tab 130. When the photographic lens 2 isturned by 40.5° relative to the correct interlock phase along thecounterclockwise direction viewed from the front side of the camera body1, as shown in FIG. 30, the lens retainer lock pin 9 projecting outthrough the pin hole 161 at the body mount 100 is inserted through thepin hole 261 at the accessory mount 200, thereby restrictingcounterclockwise rotation. It is to be noted that when the lens releasebutton (not shown) is depressed so as to cause the lens retainer lockpin 9 to retract backward relative to the body mount reference surface101 and the photographic lens 2 is rotated counterclockwise, therestricting member 262 comes in contact with the second side end 122 ofthe body-side second tab 120, thereby restricting rotation along thecounterclockwise direction.

In other words, once the photographic lens 2 is turned by 40.5° alongthe counterclockwise direction from the correct interlock phase, theaccessory mount 200 becomes engaged with the body mount 100 (engagementof the accessory-side tabs and the body-side tabs is completed) andthus, the photographic lens 2 becomes fully mounted. The rotationalangle of 40.5°, by which the photographic lens 2 is turned from thecorrect interlock phase to the phase at which mounting of thephotographic lens 2 is completed, is to be referred to as a mountingangle. In addition, the counterclockwise turning direction mentionedabove may be otherwise referred to as a mounting direction.

When the photographic lens 2 is fully mounted, the position of the pinhole 261 at the accessory mount 200 is aligned with the position of thepin hole 161 at the body mount 100. The lens retainer lock pin 9projecting out through the pin hole 161 at the body mount 100 is thusinserted through the pin hole 261.

—Dismounting the Photographic Lens 2 from the Camera Body 1—

The photographic lens 2 is dismounted from the camera body 1 through thefollowing procedure. The lens on/off button (not shown) disposed at thecamera body 1 is depressed so as to retract the lens retainer lock pin 9from the pin hole 261. As the photographic lens 2 is turned back to thecorrect interlock phase along the clockwise direction viewed from thefront side of the camera body 1 in this state, an engagement of theaccessory-side tabs and the camera body-side tabs is ceased. Namely, agap equivalent to a predetermined clearance is formed between therestricting member 262 and the first side end 111 of the body-side firsttab 120. In other words, the state shown in FIG. 29 is resumed. Sincethe body-side tabs 110 to 130 and the accessory-side tabs 210 to 230 donot interfere with each other at the correct interlock position, asexplained earlier, the photographic lens 2 can be pulled forward andseparated from the camera body 1. It is to be noted that as thephotographic lens 2, having been rotated to the correct interlock phase,is further rotated clockwise, the restricting member 262 comes intocontact with the first side end 111 of the body-side first tab 120 so asto restrict any further rotation along the clockwise direction. Alsonote that the clockwise turning direction mentioned above may beotherwise referred to as a dismounting direction.

As described above, if the user attempts to mount the photographic lens2 onto the camera body 1 while holding down the lens release button (notshown), the restricting member 262 comes in contact with the second sideend 122 of the body-side second tab 120, thereby restricting rotation ofthe photographic lens 2 along the mounting direction. In addition, whenthe photographic lens 2 currently mounted at the camera body 1 isdismounted from the camera body 1, the restricting member 262 contactsthe first side end 111 of the body-side first tab 110 so as to restrictrotation along the dismounting direction. In the description, the endsurface of the restricting member 262 that comes in contact with thesecond side end 122 of the body-side second tab 120 as the user attemptsto mount the photographic lens 2 at the camera body 1 while holding downthe lens release button (not shown) will be referred to as a mountingside end surface. In addition, the end surface of the restricting member262 that comes in contact with the first side end 111 of the body-sidefirst tab 110 as the user dismounts the photographic lens 2 from thecamera body 1 will be referred to as a dismounting side end surface.Namely, the mounting side end surface of the restricting member 262 isset apart, along the clockwise direction in FIG. 29, from the secondside end 122 of the body-side second tab 120 by an extent matching thesum of the mounting angle and the angle representing a predeterminedinterval at the accessory mount 200 inserted at the body mount 100 atthe correct interlock phase, as shown in FIG. 29. In addition, thedismounting side end surface of the restricting member 262 is set apart,along the counterclockwise direction in FIG. 29, from the first side end111 of the body-side first tab 110 by an extent matching the anglerepresenting the predetermined interval at the accessory mount 200inserted through the body mount 100 at the correct interlock phase, asshown in FIG. 29.

—Insertion of the Photographic Lens 2 at a Phase Other than the CorrectInterlock Phase—

If the user attempts to insert the photographic lens 2 at a phase otherthan the correct interlock phase, at least two tabs among the body-sidetabs 110 to 130 at the body mount 100 and at least two tabs among theaccessory-side tabs 210 to 230 at the accessory mount 200 come intocontact with each other at, at least, two contact locations, and thus,insertion of the accessory mount 200 through the body mount 100 isdisallowed (deterred) in the embodiment.

As can be surmised by viewing FIG. 29, if the user attempts to mount thephotographic lens 2 slightly offset from the correct interlock phasealong the counterclockwise direction in the figure, the rear surface 213of the accessory-side first tab 210 will come into contact with thefront surface 113 of the body-side first tab 110, the rear surface 223of the accessory-side second tab 220 will come into contact with thefront surface 123 of the body-side second tab 120, and the rear surface233 of the accessory-side third tab 230 will come into contact with thefront surface 133 of the body-side third tab 130. As a result, the threebody-side tabs 110 to 130 and the three accessory-side tabs 210 to 230will be in contact with each other and insertion of the accessory mount200 into the body mount 100 will thus be disallowed. This situation mayarise when, for instance, the accessory-side tabs 210 to 230 in FIG. 30are positioned frontward relative to the body-side tabs 110 to 130.

If the user attempts to mount the photographic lens 2 offset by agreater extent along the counterclockwise direction relative to thestate described above, the accessory-side second tab 220 will movefrontward relative to the body-side third gap 153, as shown in FIG. 31and thus, the accessory-side second tab 220 will no longer be in contactwith any of the body-side tabs 110 to 130. However, the rear surface 213of the accessory-side first tab 210 will be contact with the frontsurface 113 of the body-side first tab 110 and the rear surface 233 ofthe accessory-side third tab 230 will be contact with the front surface133 of the body-side third tab 130. In this situation, the contactachieved by the two body-side tabs among the body-side tabs 110 to 130and the two accessory-side tabs among the accessory-side tabs 210 to 230disallows insertion of the accessory mount 200 through the body mount100. The contact thus achieved by the body-side tabs 110 to 130 and theaccessory-side tabs at a total of two contact locations is indicated asthe hatched areas in FIG. 31.

A slight counterclockwise rotation of the photographic lens 2 will alterthe positional relationship of the two mounts relative to each other inFIG. 31 to a positional relationship whereby the rear surface 213 of theaccessory-side first tab 210 contacts the front surface 123 of thebody-side second tab 120. Namely, a slight counterclockwise turn of thephotographic lens 2 will allow the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 to achieve contact at three contactlocations. If, on the other hand, the photographic lens 2 in the stateshown in FIG. 31 is turned along the clockwise direction, the rearsurface 213 of the accessory-side first tab 210 and the front surface113 of the body-side first tab 110 will contact each other over a largerarea and the rear surface 233 of the accessory-side third tab 230 andthe front surface 133 of the body-side third tab 130 will contact eachother over a larger area.

In other words, FIG. 31 shows a state in which the contact of the rearsurface 213 of the accessory-side first tab 210 and the front surface113 of the body-side first tab 110 and the contact of the rear surface233 of the accessory-side third tab 230 and the front surface 133 of thebody-side third tab 130 are achieved at the two contact locations overthe smallest contact area. The rear surface 213 of the accessory-sidefirst tab 210 and the front surface 113 of the body-side first tab 110contact each other at the interlock phase shown in FIG. 31 over anangular range, assumed by viewing the body mount 100 from the front sideof the camera body 1, of 11°.

It is to be noted that there are other situations in which insertion ofthe accessory mount 200 through the body mount 100 is disallowed via atotal of two contact locations where two tabs among the body-side tabs110 to 130 and two tabs among the accessory-side tabs 210 to 230 contacteach other. Among the plurality of states in which insertion of theaccessory mount 200 through the body mount 100 is disallowed via a totalof two contact locations where two tabs among the body-side tabs 110 to130 and two tabs among the accessory-side tabs 210 to 230 achievecontact, the smallest contact area is formed at either of the twocontact locations in two specific conditions, i.e., the state shown inFIG. 31 and the state (not shown) achieved by rotating the photographiclens 2 in the state shown in FIG. 31 by 11° along the counterclockwisedirection in the figure, as described below.

If the photographic lens 2 with the two mounts assuming the specificpositional relationship relative to each other as shown in FIG. 31 isturned by 11° along the counterclockwise direction in the figure, thecontact of the rear surface 213 of the accessory-side first tab 210 andthe front surface 113 of the body-side first tab 110 will cease but therear surface 213 of the accessory-side first tab 210 will come intocontact with the front surface 123 of the body-side second tab 120. Itis to be noted that contact will also be achieved as the rear surface233 of the accessory-side third tab 230 comes into contact with thefront surface 133 of the body-side third tab 130. The rear surface 213of the accessory-side first tab 210 and the front surface 123 of thebody-side second tab 120 will contact each other over an angular range,assumed by viewing the body mount 100 from the front side of the camerabody 1, of 11°, as in the state shown in FIG. 31.

Thus, in this case too, contact will be achieved by the body-side tabs110 to 130 and the accessory-side tabs 210 to 230 at a total of twocontact locations. Among various states in which the contact is achievedby the rear surface 213 of the accessory-side first tab 210 and thefront surface 123 of the body-side second tab 120 and contact isachieved by the rear surface 233 of the accessory-side third tab 230 andthe front surface 133 of the body-side third tab 130 at a total of twocontact locations, the accessory-side tabs and the body-side tabscontact each other over the smallest area in this state.

Namely, while there are various insertion disallowed states, in whichinsertion of the accessory mount 200 through the body mount 100 isdisallowed via a total of two contact locations where two tabs among thebody-side tabs 110 to 130 and two tabs among the accessory-side tabs 210to 230 contact each other, the rear surface 213 of the accessory-sidefirst tab 210 and the front surface 113 of the body-side first tab 110contact each other over the smallest contact area in the state shown inFIG. 31. Likewise, the smallest contact area is also formed by the rearsurface 213 of the accessory-side first tab 210 and the front surface123 of the body-side second tab 120 in the insertion disallowed statewith the photographic lens 2 turned counterclockwise by 11° relative tothe state shown in FIG. 31, among the insertion disallowed states inwhich insertion of the accessory mount 200 through the body mount 100 isdisallowed via a total of two contact locations among the body-side tabs110 to 130 and two tabs among the accessory-side tabs 210 to 230 contacteach other. The interlock phase shown in FIG. 31 and the interlock phaseassumed with the photographic lens 2 turned by 11° along thecounterclockwise direction relative to the state shown in FIG. 31 areeach referred to as a specific interlock phase.

As described above, a counterclockwise rotation of the photographic lens2 in the state shown in FIG. 31 will cause the figure, the rear surface213 of the accessory-side first tab 210 to come into contact with boththe front surface 113 of the body-side first tab 110 and the frontsurface 123 of the body-side second tab 120 and cause the rear surface233 of the accessory-side third tab 230 to come into contact with thefront surface 133 of the body-side third tab 130. In other words, thebody-side tabs 110 to 130 and the accessory-side tabs 210 to 230 willachieve contact at a total of three contact locations.

As the photographic lens 2 is turned further counterclockwise in thefigure until the photographic lens 2 is rotated by 11° along thecounterclockwise direction relative to the state shown in FIG. 31, asdescribed above, the rear surface 213 of the accessory-side first tab210 and the front surface 113 of the body-side first tab 110 will ceaseto be in contact with each other and thus, the number of contactlocations where the body-side tabs 110 to 130 and the accessory-sidetabs 210 to 230 contact each other will be reduced to two.

As the photographic lens 2 is turned further along the counterclockwisedirection in the figure, the state shown in FIG. 32 will be achieved.

As can be surmised by viewing FIG. 32, a slight counterclockwise turn ofthe photographic lens 2 will alter the positional relationship shown inFIG. 32, causing the rear surface 223 of the accessory-side second tab220 to come into contact with the front surface 133 of the body-sidethird tab 130. In other words, contact will be achieved by the body-sidetabs 110 to 130 and the accessory-side tabs 210 to 230 at a total ofthree contact locations. A further counterclockwise turn of thephotographic lens 2 will cause the rear surface 233 of theaccessory-side third tab 230 to come into contact with the front surface113 of the body-side first tab 110 as well. In this situation, contactwill be achieved by the body-side tabs 110 to 130 and the accessory-sidetabs 210 to 230 over a total of four contact locations.

As the photographic lens 2 is turned further counterclockwise, the rearsurface 233 of the accessory-side third tab 230 and the front surface133 of the body-side third tab 130 will cease contact with each otherand then, the rear surface 213 of the accessory-side first tab 210 andthe front surface 123 of the body-side second tab 120, too, will ceasecontact with each other. In other words, contact will be achieved by thebody-side tabs 110 to 130 and the accessory-side tabs 210 to 230 at atotal of two contact locations under these circumstances, as shown inFIG. 33.

A further counterclockwise turn of the photographic lens 2 in the stateshown in FIG. 33 will cause a decrease in both the contact area overwhich the rear surface 223 of the accessory-side second tab 220 and thefront surface 133 of the body-side third tab 130 are in contact witheach other and the contact area over which the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 are contact with each other. In other words, FIG. 33 showsa state in which the contact of the rear surface 223 of theaccessory-side second tab 220 and the front surface 133 of the body-sidethird tab 130 and the contact of the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 are achieved at two contact locations over the largestcontact area.

FIG. 34 shows a state achieved by further turning the photographic lens2 along the counterclockwise direction relative to the state shown inFIG. 33. Among various states in which the rear surface 223 of theaccessory-side second tab 220 and the front surface 133 of the body-sidethird tab 130 contact each other and the rear surface 233 of theaccessory-side third tab 230 and the front surface 113 of the body-sidefirst tab 110 contact each other at a total of two contact locations,the accessory-side tabs and the body-side tabs contact each other overthe smallest area in this state.

A slight counterclockwise turn of the photographic lens 2 relative tothe state shown in FIG. 34 will allow the rear surface 213 of theaccessory-side first tab 210 and the front surface 133 of the body-sidethird tab 130 to come into contact with each other. At this time,contact will be achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of three contact locations. Asthe photographic lens 2 in this state is turned further along thecounterclockwise direction in the figure, the rear surface 233 of theaccessory-side third tab 230 and the front surface 123 of the body-sidesecond tab 120 will come into contact with each other. In this state,contact will be achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of four contact locations.

As the photographic lens 2 in this state is turned further along thecounterclockwise direction in the figure, the rear surface 223 of theaccessory-side second tab 220 and the front surface 133 of the body-sidethird tab 130 will cease contact with each other. At this time, contactwill be achieved by the body-side tabs 110 to 130 and the accessory-sidetabs 210 to 230 at a total of three contact locations. As shown in FIG.35, when the photographic lens 2 is further turned along thecounterclockwise direction, the rear surface 233 of the accessory-sidethird tab 130 ceases contact with the front surface 113 of the body-sidefirst tab 110. At this point, the body-side tabs 110 through 130 and theaccessory-side tabs 210 through 230 contact each other at a total of twocontact locations.

As the photographic lens 2 is slightly turned along the counterclockwisedirection relative to the state shown in FIG. 35, the rear surface 223of the accessory-side second tab 220 and the front surface 113 of thebody-side first tab 110 will come into contact with each other. At thistime, the body-side tabs 110 through 130 and the accessory-side tabs 210through 230 contact each other at a total of three contact locations. Asthe photographic lens 2 is turned further along the counterclockwisedirection in the figure, the correct interlock phase shown in FIG. 29will be reestablished and any contact (interference) between thebody-side tabs 110 to 130 and the accessory-side tabs 210 to 230 willcease.

—Rationale for Disposing the Restricting Member 262 at theAccessory-Side Second tab 220—

In the embodiment, the restricting member 262 is disposed at theaccessory-side second tab 220 so as to achieve the following advantages.

(1) Among the three tabs (210, 220 and 230) present on theaccessory-side, the accessory-side second tab 220 ranges over theshortest distance along the circumference of the accessory mount 200. Inother words, the accessory-side second tab 220 assumes the shortestcircular arc length among the three tabs. This means that theexchangeable lens 2 can be mounted at the camera body 1 at the correctinterlock phase simply by rotating the exchangeable lens 2 by an extentmatching the circular arc length of the accessory-side second tab 220.Likewise, the exchangeable lens 2 can be dismounted from the camera body1 simply by rotating the exchangeable lens 2 (along the directionopposite from the direction in which it is rotated during the mountingoperation) by the extent matching the circular arc length of theaccessory-side second tab 220. Namely, by disposing the restrictingmember at the accessory-side tab 220, the extent to which the user needsto rotate the accessory to mount or dismount it can be minimized.Consequently, the rotating operation onus placed on the user whilemounting or dismounting the accessory (exchangeable lens 2) can bereduced and the length of time required to mount or dismount theaccessory (exchangeable lens 2) can be reduced as well.

(2) In the embodiment, a single restricting member 262 is used both torestrict the range of rotation when mounting the accessory and restrictthe range of rotation when dismounting the accessory, instead of usingtwo separate restricting members in correspondence to the mountingoperation and the dismounting operation. As a result, the number ofrequired parts can be minimized and the mount structure can besimplified.

(3) The restricting member 262 located at the second tab 220 physicallycontacts a tab end of a body-side tab, which is present at a positionwhere damage does not occur readily while the camera is in use. In otherwords, the restricting member 262 restricts the range of rotation of theaccessory (exchangeable lens 2) being mounted or dismounted by cominginto physical contact with an end portion (an end portion of thebody-side tab) located at a less vulnerable position.

This point is explained in further detail below. The accessory-sidesecond tab 220 at which the restricting member 262 is disposed movesthrough the body-side second gap 152 with the narrowest angular rangealong the circumferential edge of the circular opening at the camerabody 1 while the photographic lens 2 is being mounted (at the correctinterlock phase). The angular range of the body-side second group 152along the circumferential edge of the circular opening at the camerabody 1 is 47.5°. This means that the accessory-side first tab 210 (withits angular range of 58.5°) and the accessory-side third tab 230 (withits angular range of 71.5°), assuming greater angular ranges than the47.5° angular range cannot pass through the body-side second gap 152.Thus, at any phase other than the correct interlock phase, there is norisk of the accessory-side first tab 210 or the accessory-side third tab230 moving into the body-side second gap 152 and consequently, the firstside end 111 of the body-side first tab 110 and the second side end 122of the body-side second tab 120, which define the angular range of thebody-side second gap 152, are less likely to be damaged.

The following problem would arise if the first side end 111 of thebody-side first tab 110 and the second side end 122 of the body-sidesecond tab 120 were susceptible to damage.

As explained earlier, the first side end 111 of the body-side first tab110 comes in contact with the restricting member 262 while thephotographic lens 2 is being dismounted from the camera body 1 so thatthe photographic lens 2 does not rotate along the dismounting directionany more than necessary. Thus, if the first side end 111 of thebody-side first tab 110 becomes damaged and, for instance, chipped, thephotographic lens 2 will be allowed to rotate along the dismountingdirection further than necessary. Under such circumstances, the secondside end 212 of the accessory-side first tab 210 may move furtherrearward relative to the body-side third tab 130 or the second side end232 of the accessory-side third tab 230 may move further rearwardrelative to the body-side second tab 120, causing the photographic lens2 to jam at the camera body 1.

As explained earlier, the second side end 122 of the body-side secondtab 120 comes in contact with the restricting member 262 while thephotographic lens 2 is being mounted at the camera body 1 by the userholding down the lens release button so as to ensure that thephotographic lens 2 is not allowed to rotate along the mountingdirection any further than necessary. As the photographic lens 2 mountedat the camera body 1 while holding down the lens release button (notshown) is turned along the mounting direction until the restrictingmember 262 comes in contact with the second side end 122 of thebody-side second tab 120, at the position of the lens retainer lock pin9 and the position of the pinhole 261 at the accessory mount 200 maybecome slightly offset relative to each other.

However, since the lens retainer lock pin 9 has a rounded end, theaccessory mount 200, having rotated by a greater extent than necessaryalong the mounting direction, will be repositioned to assume the correctphase, as the lens retainer lock pin 9, driven with the force impartedfrom the spring (not shown) passes through the pin hole 261 once theuser releases the lens release button, as long as the offset of the pinhole 261 is slight. Otherwise, as the user releases the lens releasebutton and the photographic lens 2 is caused to move back slightly, thelens retainer lock pin 9 will slip through the pin hole 261, therebysetting the accessory mount 200 at the correct phase.

If the second side end 122 at the body-side second tab 120 becomesdamaged, however, the position of the lens retainer lock pin 9 and theposition of the pin hole 261 at the accessory mount 200 may becomeoffset relative to each other by a significant extent as thephotographic lens 2 is mounted at the camera body 1 while the lensrelease button (not shown) is held down. Under such circumstances, evenif the user releases the lens release button, the lens retainer lock pin9 will be unable to pass through the pin hole 261 and thus the accessorymount 200, having turned along the mounting direction by an excessiveextent, will not resume the correct phase. As a result, problems such asdisabled photographing operation due to an offset of electrical contactpoints (not shown) via which signals and the like are exchanged by thephotographic lens 2 and the camera body 1, will occur.

In the embodiment, it is ensured that the first side end 111 of thebody-side first tab 110 and the second side end 122 of the body-sidesecond tab 120 are less susceptible to damage as described above, so asto prevent such problems and provide a more reliable camera system.

—Positional Relation Between the Restricting Member 262 and the Pin Hole261—

As shown in FIG. 8, in the mounting complete state, the position of therestricting member 262 is substantially opposite from the position ofthe pin hole 261, that is, the position of the pin hole 161, across thefitting portion 202 which is not show in FIG. 8, i.e., the optical axisof the photographic lens 2. In other words, the restricting member 262and the pin hole 261 (or the pin hole 161) are arranged so that they aresubstantially axisymmetrically disposed with respect to the optical axiswhen viewed along the optical axis of the photographic lens 2.

If, for instance, a gap between the inner circumferential surface 102 ofthe cylindrical body mount 100 and the fitting portion 202 of theaccessory mount 200 is large, the accessory mount 200, that is, thephotographic lens 2, is capable of swinging with respect to the bodymount 100, that is, the camera body 1, about the lens retainer lock pin9 in a direction as indicated by an arrow A. It is to be noted that theswinging of the accessory mount 200 is exaggerated in FIG. 16 for thesake of illustration.

The swinging about the lens retainer lock pin 9 causes the positionfurthest from the lens retainer lock pin 9 to be displaced by a largestdistance. Therefore, in the present embodiment, the largest positionalchange by the swinging around the lens retainer lock pin 9 occurs nearthe restricting member 262 which is substantially opposite from the pinhole 261 across the fitting portion 202 (or the optical axis of thephotographic lens 2). The direction of the positional change by theswinging around the lens retainer lock pin 9 is a tangential directionsof a circle centered at the lens retainer lock pin 9 as indicated by anarrow B in FIG. 36.

In other words, the direction of the positional change caused by theswinging around the lens retainer lock pin 9 near the restricting member262 substantially corresponds to a direction in which the restrictingmember 262 comes in contact with and separates from the second side end122 of the body-side second tab 120. As described above, in the mountingcompletion state of the photographic lens 2, the mounting side endsurface of the restricting member 262 is merely set apart from thesecond side end 122 of the body-side second tab 120 by a predeterminedclearance. Thus, in the present embodiment, the positional change in thephotographic lens 2 caused by the swinging around the lens retainer lockpin 9 can be reduced effectively by the restricting member 262 and thesecond side end 122 of the body-side second tab 120 even when the gapbetween the cylindrical inner circumferential surface 102 of the bodymount 100 and the fitting portion 202 of the accessory mount 200 becomeslarge.

It is to be noted that as long as the swinging movement centered on thelens retainer lock pin 9 can be effectively deterred, the restrictingmember 262 may assume a phase other than that described above in thefully mounted state. This point will be explained in reference to themodel presented in FIG. 37. ΔR in the model in FIG. 37 represents ahypothetical difference between the radius of the cylindrical camerabody mount 100 measured to its inner circumferential surface 102 and theradius of the accessory mount 200 measured at its fitting portion 202.In addition, θ in the model presented in FIG. 37 denotes the angleformed around the center of the circle defined by the innercircumferential surface 102 (fitting portion 202), i.e., the anglecentered on the optical axis, which represents the position of therestricting member 262 in the fully mounted state, measured along theclockwise direction relative to the nine o'clock direction in thefigure. In this model, it is hypothesized that ΔR is equal to onethousandth of R (=D/2), representing a virtual radius of the cylindricalcamera body mount 100 measured at its inner circumferential surface 101and also of the accessory mount 200 measured at its fitting portion 202.It is also hypothesized that the distance from the center of the circledefined by the inner circumferential surface 102 to the center of thelens retainer lock pin 9 is R+L and that L is 0.14 times R (i.e.,L/R=0.14).

In conjunction with the hypothetical dimensions assumed as describedabove, the distance by which the restricting member 262 moves on thecircumference of the circle with the radius R along a tangentialdirection as the fitting portion 202, the center of which has beenaligned with the center of the circle defined by the innercircumferential surface 102, swings upward around the lens retainer lockpin 9 by an extent allowed in correspondence to the difference ΔRbetween the radii explained above, is referred to as a “shift quantity”.The value obtained by dividing the “shift quantity” by the radius R forpurposes of non-dimensional representation is referred to as a “shiftquantity ratio”. The relationship between the “shift quantity ratio” andθ can be graphed as the curve shown in FIG. 38. Since the radius R is aconstant, the greater a value of the “shift quantity ratio”, the greaterthe “shift quantity” relative to the extent of swinging movement of thefitting portion 202 centered on the lens retainer lock pin 9. Thus, thegreater the value of the shift quantity ratio, the more effectively canthe swinging movement of the fitting portion 202 around the center ofthe lens retainer lock pin 9, be deterred by the restricting member 262coming into contact with the second side end 122 of the body side secondtab 120. As the graph in FIG. 38 indicates, the “shift quantity ratio”assumes a smaller value when θ assumes a greater value and that once thevalue of θ exceeds 30°, the “shift quantity ratio” decreases markedly.Accordingly, when the hypothetical dimensions are assumed as describedabove, the phase of the restricting member 262 in the fully mountedstate should be set by ensuring that θ does not assume a value exceeding30°.

—Accessory-Side Third Tab 230—

As explained earlier, located near the first side end 231 of theaccessory-side third tab 230, the front surface 234 is pressed by thespring 136 at the body-side third tab 130, and whenever an excessiveexternal force is applied, the front surface 234 will come into contactwith the contact portion 135. This means that when the photographic lens2 is mounted at the camera body 1, the force applied to lock thephotographic lens 2 to the camera body 1 will be applied primarily tothe area near the first side end 231 at the accessory-side third tab230.

—Body-Side First Tab 110—

When contact is achieved by the body-side tabs 110 to 130 and theaccessory-side tabs 210 to 230 at a total of two contact locations withthe body-side first tab 110 in contact with an accessory-side tab at oneof the contact locations, the body-side first tab 110 invariablycontacts the accessory-side tab 210, 220 or 230 on the side where itsfirst side end 111 is located (i.e., at the front surface 113 near thefirst side end 111), rather than on the side where its second side end112 is located (i.e., at the front surface 113 near the second side end112), as shown in FIGS. 31, 33 and 34. In other words, when contact isachieved by the body-side tabs 110 to 130 and the accessory-side tabs210 to 230 at a total of two contact locations and the body-side firsttab 110 achieves contact at one of the contact locations, the functionof preventing erroneous insertion is achieved in the area near the firstside end 111 of the body-side first tab 110.

The spring 116 is disposed adjacent to the contact portion 115 at thebody-side first tab 110 over the area near its second side end 112.Namely, the function of locking the photographic lens 2 having beenmounted at the camera body 1 is achieved over the area near the secondside end 112 of the body-side first tab 110

In summary, the body-side first tab 110 is formed so that differentfunctions are achieved in the area near the first side end 111 and thearea near the second side end 112 along the direction in which thebody-side first tab 110 extends.

The camera body 1 and the photographic lens 2 achieved in the secondembodiment as described above achieve the following advantages inaddition to the advantages of the first embodiment.

(1) The restricting member 262 and the pin hole 261 (the pin hole 161)are arranged so that they are disposed substantially axisymmetricallywith respect to the optical axis when viewed along the optical axis ofthe photographic lens 2. In this manner, the positional change in thephotographic lens 2 caused by the swinging around the lens retainer lockpin 9 can be reduced effectively by the restricting member 262 and thesecond side end 112 of the body-side first tab 110 even when the gapbetween the cylindrical inner circumferential surface 102 of the bodymount 100 and the fitting portion 202 of the accessory mount 200 becomeslarge.

(2) In the present embodiment, the restricting member 262 is disposed atthe accessory-side second tab 220 which ranges over the shortestdistance along the circumference of the accessory mount 200 or assumesthe shortest circular arc length. Consequently, the rotating operationonus placed on the user while mounting or dismounting the accessory canbe reduced and the length of time required to mount or dismount theaccessory can be reduced as well.

(3) In the embodiment, a single restricting member 262 is used both torestrict the range of rotation when mounting the accessory and restrictthe range of rotation when dismounting the accessory. As a result, thenumber of required parts can be minimized and the mount structure can besimplified.

(4) In the embodiment, the restricting member 262 located at the secondtab 220 physically contacts a tab end of a body-side tab, which ispresent at a position where damage does not occur readily. In otherwords, the restricting member 262 restricts the range of rotation of theaccessory being mounted or dismounted by coming into physical contactwith an end portion (an end portion of the body tab) located at a lessvulnerable position. As a result, a rotation regulating structureassuring a high level of durability is achieved, which, in turn, makesit possible to improve the durability of the bayonet-type mountstructure.

In other words, the body-side second gap 152 is formed so as to assume anarrower angular range along the circumferential edge of the circularopening at the camera body 1 compared to the other body-side gaps 151and 153, so as to ensure that the accessory-side first tab 210 or theaccessory-side third tab 230 does not move into the body-side second gap152 at any phase other than the correct interlock phase and thus,improve the durability of the bayonet mount structure as describedabove.

—Variations—

(1) While the accessory-side tabs 210 to 230 are fixed onto the mainbody of the photographic lens 2 and the photographic lens 2 is mountedor dismounted by turning it along the mounting direction or thedismounting direction relative to the camera body 1 in the embodimentsdescribed above, the present invention is not limited to this example.For instance, the present invention may be adopted in conjunction with astructure that includes accessory-side tabs 210 to 230 rotatablydisposed relative to the main body of the photographic lens 2 and allowsthe photographic lens 2 to be mounted at the camera body 1 simply byrotating the accessory-side tabs 210 to 230 alone along the mountingdirection once the photographic lens 2 is positioned at the correctinterlock phase.

FIGS. 20A and 20B present external views of a photographic lens 20 withaccessory-side tabs 210 to 230 formed thereat so that they are able torotate relative to the main body of the photographic lens 2. Thephotographic lens 20 includes a lens barrel 21, a bayonet tube 22disposed rotatably relative to the lens barrel 21, at whichaccessory-side tabs 210 to 230 are disposed, and an operation ring 23via which the bayonet tube 22 is rotated relative to the lens barrel 21.It is to be noted that in FIGS. 20A and 20B and other figures inreference to which the following description is provided, the samereference numerals are assigned to members similar to those alreadydescribed so as to preclude the necessity for a repeated explanationthereof.

FIG. 21 presents an external view of the lens barrel 21, whereas FIGS.22A to 22D schematically illustrate the structure of the photographiclens 20. As shown in FIG. 21, a fitting groove 21 a at which theoperation ring 23 fits is formed at the rear of the lens barrel 21. Anelongated hole 21 b, through which a pin 24 connecting the operationring 23 with the bayonet tube 22 is allowed to move, is formed at thebottom of the fitting groove 21 a. As indicated in the sectional viewspresented in FIGS. 22A and 22D, the operation ring 23 fits into thefitting groove 21 a at the lens barrel 21 and the operation ring 23 andthe bayonet tube 22 are linked with each other via the pin 24. Referencenumeral 25 indicates a lens. As the operation ring 23 is rotatedrelative to the lens barrel 21 in the photographic lens 20 structured asdescribed above, the bayonet tube 22, i.e., the accessory-side tabs 210to 230, turns together with the operation ring 23 relative to the lensbarrel 21. The photographic lens 20 assuming this structure can bemounted at the camera body 1 without having to turn the lens barrel 21,by simply operating the operation ring 23 to turn the bayonet tube 22alone along the mounting direction once the photographic lens 20 ispositioned at the correct interlock phase. It is to be noted that FIG.22D is a sectional view taken along C-C in FIG. 22A.

(2) The photographic lenses 2 and 20 described above each represent anexample of a camera accessory. Namely, the present invention is notlimited to these examples and may be adopted in conjunction with any ofvarious types of camera accessories such as a converter lens used toadjust the focal length or an adapter used to adjust the distance fromthe photographic lens mount surface to the image capturing plane, aslong as it includes an accessory mount 200, which can be engaged with acamera body mount 100.

(3) While the restricting member 262 described above is headed pindisposed at the accessory mount 200, an area near the second side end222, for instance, may be formed in a specific shape so as to functionas a restricting member 262, instead of providing a separate member.Namely, an area near the second side end 222 may be formed to assume ashape that will allow the area to function as a restricting member 262through injection molding at an accessory mount 200 constituted with aresin injection mold. In addition, the restricting member 262 may beconstituted with two pins; a first pin that includes a mounting side endsurface, such as that explained earlier, and a second pin, differentfrom the first pin, which includes a dismounting side end surface suchas that described earlier. As a further alternative, instead ofdisposing separate members such as the first pin and the second pin, anarea near the second side end 222 may be formed so as to assume shapesresembling a first pin and a second pin.

(4) The camera body mount 100 described above may be disposed at thephotographic lens 2 and the accessory mount 200 described above may bedisposed at the camera body 1.

(5) An explanation has been given above in reference to the embodimentson an example in which the present invention is adopted in a camerasystem comprising the camera body 1 and the exchangeable lens 2.However, the present invention is not limited to this example and may beadopted in any system other than a camera system, as long as it includesa mount at which the exchangeable lens 2 can be detachably mounted. Sucha system may be, for instance, an electronic device such as a projector.A system similar to those described in reference to the embodiments canbe achieved by equipping the projector with an exchangeable projectionlens that can be detachably mounted.

(6) Various embodiments and variations described above may be adopted incombination.

It is to be noted that the present invention is not limited to specificstructural features of the embodiments described above in any waywhatsoever and that a camera accessory, which can be detachably mountedat a camera body equipped with a camera body mount and includes anaccessory mount assuming a bayonet structure with first through thirdtabs set over intervals in a circumferential direction running along acircumference of a circle with a specific diameter and projectingradially from the circumference, characterized in that the accessorymount is allowed to be inserted through the camera body mount withoutany of the first through third tabs being hindered by any of threecamera body-side tabs at the camera body mount, as long as the accessorymount is inserted at the camera body mount at a correct interlock phase,that the first through third tabs extend along the circumferentialdirection over varying lengths, with the first tab extending over agreatest length along the circumferential direction among the firstthrough third tabs and the third tab extending over a smallest lengthalong the circumferential direction among the first through third tabs,that the accessory mount includes a restricting member disposed near thethird tab, a fitting portion used to align an optical axis of theaccessory mount with an optical axis of the camera body and a lock pinhole through which a lock pin, retractably disposed at the camera body,is inserted so as to lock the camera accessory in a fully mounted state,and that the restricting member is disposed at a position assumed on aside substantially opposite from the lock pin hole across the fittingportion, otherwise adopting any of various structures, are all withinthe scope of the present invention.

According to the present invention described above, backlash between acamera accessory and a camera body can be effectively prevented.

The above described embodiments are examples and various modificationscan be made without departing from the scope of the invention.

What is claimed is:
 1. A camera accessory that can be detachably mountedat a camera body that includes a camera body mount, the camera accessoryincluding a cylindrical member having an optical path in its innercircumferential side and being equipped with an accessory mount assuminga bayonet structure with a first tab, a second tab and a third tabdisposed at a circumferential surface of the cylindrical member overintervals in a circumferential direction running along thecircumferential surface and projecting outward from the circumferentialsurface along a radial direction, wherein: the first tab, the second taband the third tab are disposed at the accessory mount so that the firsttab, the second tab and the third tab can be inserted through the camerabody mount without any of the first tab, the second tab and the thirdtab being hindered by any of three camera body-side tabs at the camerabody mount when the accessory mount is inserted into the camera bodymount at a predetermined interlock position; the first tab, the secondtab and the third tab extend over varying lengths along thecircumferential direction; the first tab extends over a greatest lengthalong the circumferential direction among the first tab, the second taband the third tab; the third tab extends over a smallest length alongthe circumferential direction among the first tab, the second tab andthe third tab; the accessory mount includes: a restricting memberdisposed adjacent to the third tab such that the third tab overlaps therestricting member as viewed along a direction parallel to an axialdirection of the camera accessory, and a lock pin hole through which alock pin disposed at the camera body is inserted so as to restrictrotation of the camera accessory relative to the camera body, the lockpin hole being disposed between the first tab and the second tab in thecircumferential direction, and being disposed closer to the first tabthan to the second tab, wherein: the restricting member is disposed at aposition assumed on a side substantially opposite from the lock pin holeacross a center of the cylindrical member, and when the first tab, thesecond tab and the third tab are inserted at the predetermined interlockposition and completely mounted at the camera body mount, therestricting member and the lock pin hole are disposed substantiallyalong a horizontal axis parallel to a bottom surface of the camera body.2. The camera accessory according to claim 1, wherein: when the firsttab, the second tab and the third tab are rotated along thecircumference in a first rotating direction in order to mount theaccessory mount, having been inserted at the predetermined interlockposition, at the camera body mount, the restricting member comes intocontact with a side end of one camera body-side tab among the camerabody-side tabs, thereby restricting a range of rotation in the firstrotating direction; and when the first tab, the second tab and the thirdtab are rotated along the circumference in a second rotating directionopposite from the first rotating direction in order to dismount theaccessory mount from the camera body mount, the restricting member comesinto contact with a side end of a camera body-side tab different fromthe one camera body-side tab, thereby restricting a rotation range inthe second rotating direction.
 3. The camera accessory according toclaim 1, wherein: insertion of the accessory mount through the camerabody mount is disallowed if the accessory mount is positioned at aposition other than the predetermined interlock position, with at leasttwo tabs among the first tab, the second tab and the third tab cominginto contact with at least two of the camera body-side tabs.
 4. Thecamera accessory according to claim 1, wherein: the first tab at theaccessory mount having been inserted at the predetermined interlockposition and completely mounted at the camera body mount overlaps acamera body-side tab assuming an uppermost position when the camera bodyis set with a longitudinal orientation achieved by rotating the uprightcamera body assuming a lateral orientation by approximately 90°.
 5. Thecamera accessory according to claim 1, wherein: the first tab, thesecond tab and the third tab are fixed to a main body of the cameraaccessory.
 6. The camera accessory according to claim 1, wherein: thefirst tab, the second tab and the third tab are rotatably disposed so asto be allowed to rotate along the circumferential direction relative toa main body of the camera accessory.
 7. The camera accessory accordingto claim 1, wherein: the first tab, the second tab and the third tab aremade up with a tab present over an angular range of approximately 56.5°to approximately 115°, a tab present over an angular range ofapproximately 172.5° to approximately 214.5° and a tab present over anangular range of approximately 272° to approximately 343.5° at theaccessory mount having been mounted at the body mount, along a clockwisedirection relative to a nine o'clock direction viewed from a mountingside of the camera accessory onto the camera body mount.
 8. The cameraaccessory according to claim 7, wherein: when the first tab, the secondtab and the third tab are rotated along the circumferential direction byapproximately 40.5° in order to completely mount the accessory mount,having been inserted at the predetermined interlock position, with thecamera body mount, the accessory mount becomes completely mounted at thecamera body mount.
 9. A camera accessory that can be detachably mountedat a camera body that includes a camera body mount, the camera accessoryincluding a cylindrical member having an optical path in its innercircumferential side, an accessory mount assuming a bayonet structurewith a first tab, a second tab and a third tab disposed at acircumferential surface of the cylindrical member over intervals in acircumferential direction running along the circumferential surface andprojecting outward from the circumferential surface along a radialdirection, and a lens, wherein: the first tab, the second tab and thethird tab are disposed at the accessory mount so that the first tab, thesecond tab and the third tab can be inserted through the camera bodymount without any of the first tab, the second tab and the third tabbeing hindered by any of three camera body-side tabs at the camera bodymount, when the accessory mount is inserted into the camera body mountat a predetermined interlock position; the first tab, the second tab andthe third tab extend over varying lengths along the circumferentialdirection; the first tab extends over a greatest length along thecircumferential direction among the first tab, the second tab and thethird tab; the third tab extends over a smallest length along thecircumferential direction among the first tab, the second tab and thethird tab; the accessory mount includes: a restricting member disposedadjacent to the third tab, such that the third tab overlaps therestricting member as viewed along a direction parallel to an axialdirection of the camera accessory, and a lock pin hole through which alock pin disposed at the camera body is inserted so as to restrictrotation of the camera accessory relative to the camera body, the lockpin hole being disposed between the first tab and the second tab in thecircumferential direction, and being disposed closer to the first tabthan to the second tab, wherein: the restricting member is disposed at aposition assumed on a side substantially opposite from the lock pin holeacross an optical axis of the lens, and when the first tab, the secondtab and the third tab are inserted at the predetermined interlockposition and completely mounted at the camera body mount, therestricting member and the lock pin hole are disposed substantiallyalong a horizontal axis parallel to a bottom surface of the camera body.10. A camera accessory that can be detachably mounted at a camera body,with the camera body comprising a first cylindrical member provided withan opening of the camera body, and a camera body mount assuming abayonet structure and including a first camera body-side tab, a secondcamera body-side tab and a third camera body-side tab disposed at acircumferential surface of the first cylindrical member over intervalsin a circumferential direction running along the circumferentialsurface, projecting inward from the circumferential surface along aradial direction, and extending over varying lengths along thecircumferential direction, and a first camera body-side gap, a secondcamera body-side gap and a third camera body-side gap provided betweenthe three camera body-side tabs and extending over varying lengths alongthe circumferential direction, and with the camera accessory comprisinga second cylindrical member having an optical path in its innercircumferential side and being equipped with an accessory mount assuminga bayonet structure with a first accessory-side tab, a secondaccessory-side tab and a third accessory-side tab disposed at acircumferential surface of the second cylindrical member over intervalsin a circumferential direction running along the circumferential surfaceand projecting outward from the circumferential surface along a radialdirection, wherein: the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab are disposed at theaccessory mount so that the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab can be insertedthrough the three camera body-side gaps without any of the firstaccessory-side tab, the second accessory-side tab and the thirdaccessory-side tab being hindered by any of the three camera body-sidetabs when the accessory mount is inserted into the camera body mount ata predetermined interlock position; the first accessory-side tab isdisposed at the accessory mount so that the first accessory-side tab canbe inserted through the first camera body-side gap having a longestlength extending along the circumferential direction of thecircumferential surface of the first cylindrical member among the threecamera body-side gaps when the accessory mount is inserted into thecamera body mount at the predetermined interlock position; the secondaccessory-side tab is disposed at the accessory mount so that the secondaccessory-side tab can be inserted through the second camera body-sidegap among the three camera body-side gaps when the accessory mount isinserted into the camera body mount at the predetermined interlockposition; the third accessory-side tab is disposed at the accessorymount so that the third accessory-side tab can be inserted through thethird camera body-side gap having a shortest length extending along thecircumferential direction of the circumferential surface of the firstcylindrical member among the three camera body-side gaps when theaccessory mount is inserted into the camera body mount at thepredetermined interlock position; the accessory mount includes: arestricting member disposed adjacent to the third accessory-side tab,such that the third accessory-side tab overlaps the restricting memberas viewed along a direction parallel to an axial direction of the cameraaccessory, and a lock pin hole through which a lock pin disposed at thecamera body is inserted so as to restrict rotation of the cameraaccessory relative to the camera body, the lock pin hole being disposedbetween the first accessory-side tab and the second accessory-side tabin the circumferential direction, and being disposed closer to the firstaccessory-side tab than to the second accessory-side tab, wherein: therestricting member is disposed at a position assumed on a sidesubstantially opposite from the lock pin hole across a center of thesecond cylindrical member, and when the first tab, the second tab andthe third tab are inserted at the predetermined interlock position andcompletely mounted at the camera body mount, the restricting member andthe lock pin hole are disposed substantially along a horizontal axisparallel to a bottom surface of the camera body.
 11. A camera accessorythat can be detachably mounted at a camera body, with the camera bodycomprising a first cylindrical member provided with an opening of thecamera body, and a camera body mount assuming a bayonet structure andincluding a first camera body-side tab, a second camera body-side taband a third camera body-side tab disposed at a circumferential surfaceof the first cylindrical member over intervals in a circumferentialdirection running along the circumferential surface, projecting inwardfrom the circumferential surface along a radial direction, and extendingover varying lengths along the circumferential direction, and a firstcamera body-side gap, a second camera body-side gap and a third camerabody-side gap provided between the three camera body-side tabs andextending over varying lengths along the circumferential direction, andwith the camera accessory comprising a second cylindrical member havingan optical path in its inner circumferential side and being equippedwith an accessory mount assuming a bayonet structure with a firstaccessory-side tab, a second accessory-side tab and a thirdaccessory-side tab disposed at a circumferential surface of the secondcylindrical member over intervals in a circumferential direction runningalong the circumferential surface and projecting outward from thecircumferential surface along a radial direction, wherein: the firstaccessory-side tab, the second accessory-side tab and the thirdaccessory-side tab are disposed at the accessory mount so that the firstaccessory-side tab, the second accessory-side tab and the thirdaccessory-side tab can be inserted through the three camera body-sidegaps without any of the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab being hindered byany of the three camera body-side tabs when the accessory mount isinserted into the camera body mount at a predetermined interlockposition; the first accessory-side tab is disposed at the accessorymount so that the first accessory-side tab can be inserted through thefirst camera body-side gap, having a central angle of approximately78.5° which represents a range extending along the circumferentialdirection in the circumferential surface of the first cylindricalmember, when the accessory mount is inserted into the camera body mountat the predetermined interlock position; the second accessory-side tabis disposed at the accessory mount so that the second accessory-side tabcan be inserted through the second camera body-side gap, having acentral angle of approximately 61° which represents a range extendingalong the circumferential direction in the circumferential surface ofthe first cylindrical member, when the accessory mount is inserted intothe camera body mount at the predetermined interlock position; the thirdaccessory-side tab is disposed at the accessory mount so that the thirdaccessory-side tab can be inserted through the third camera body-sidegap, having a central angle of approximately 47.5° which represents arange extending along the circumferential direction in thecircumferential surface of the first cylindrical member, when theaccessory mount is inserted into the camera body mount at thepredetermined interlock position; the accessory mount includes: arestricting member disposed adjacent to the third accessory-side tab,such that the third accessory-side tab overlaps the restricting memberas viewed along a direction parallel to an axial direction of the cameraaccessory, and a lock pin hole through which a lock pin disposed at thecamera body is inserted so as to restrict rotation of the cameraaccessory relative to the camera body, the lock pin hole being disposedbetween the first accessory-side tab and the second accessory-side tabin the circumferential direction, and being disposed closer to the firstaccessory-side tab than to the second accessory-side tab, wherein: therestricting member is disposed at a position assumed on a sidesubstantially opposite from the lock pin hole across a center of thesecond cylindrical member, and when the first tab, the second tab andthe third tab are inserted at the predetermined interlock position andcompletely mounted at the camera body mount, the restricting member andthe lock pin hole are disposed substantially along a horizontal axisparallel to a bottom surface of the camera body.
 12. A camera accessorythat can be detachably mounted at a camera body, with the camera bodycomprising a first cylindrical member provided with an opening of thecamera body, and a camera body mount assuming a bayonet structure andincluding a first camera body-side tab, a second camera body-side taband a third camera body-side tab disposed at a circumferential surfaceof the first cylindrical member over intervals in a circumferentialdirection running along the circumferential surface, projecting inwardfrom the circumferential surface along a radial direction, and extendingover varying lengths along the circumferential direction, and a firstcamera body-side gap, a second camera body-side gap and a third camerabody-side gap provided between the three camera body-side tabs andextending over varying lengths along the circumferential direction, andwith the camera accessory comprising a second cylindrical member havingan optical path in its inner circumferential side, an accessory mountassuming a bayonet structure with a first accessory-side tab, a secondaccessory-side tab and a third accessory-side tab disposed at acircumferential surface of the second cylindrical member over intervalsin a circumferential direction running along the circumferential surfaceand projecting outward from the circumferential surface along a radialdirection, and a lens, wherein: the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab are disposed at theaccessory mount so that the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab can be insertedthrough the three camera body-side gaps without any of the firstaccessory-side tab, the second accessory-side tab and the thirdaccessory-side tab being hindered by any of the three camera body-sidetabs when the accessory mount is inserted into the camera body mount ata predetermined interlock position; the first accessory-side tab isdisposed at the accessory mount so that the first accessory-side tab canbe inserted through the first camera body-side gap, having a longestlength extending along the circumferential direction of thecircumferential surface of the first cylindrical member among the threecamera body-side gaps, when the accessory mount is inserted into thecamera body mount at the predetermined interlock position; the secondaccessory-side tab is disposed at the accessory mount so that the secondaccessory-side tab can be inserted through the second camera body-sidegap among the three camera body-side gaps when the accessory mount isinserted into the camera body mount at the predetermined interlockposition; the third accessory-side tab is disposed at the accessorymount so that the third accessory-side tab can be inserted through thethird camera body-side gap, having a shortest length extending along thecircumferential direction of the circumferential surface of the firstcylindrical member among the three camera body-side gaps, when theaccessory mount is inserted into the camera body mount at thepredetermined interlock position; the accessory mount includes: arestricting member disposed adjacent to the third accessory-side tab,such that the third accessory-side tab overlaps the restricting memberas viewed along a direction parallel to an axial direction of the cameraaccessory, and a lock pin hole through which a lock pin disposed at thecamera body is inserted so as to restrict rotation of the cameraaccessory relative to the camera body, the lock pin hole being disposedbetween the first accessory-side tab and the second accessory-side tabin the circumferential direction, and being disposed closer to the firstaccessory-side tab than to the second accessory-side tab, wherein: therestricting member is disposed at a position assumed on a sidesubstantially opposite from the lock pin hole across an optical axis ofthe lens, and when the first tab, the second tab and the third tab areinserted at the predetermined interlock position and completely mountedat the camera body mount, the restricting member and the lock pin holeare disposed substantially along a horizontal axis parallel to a bottomsurface of the camera body.
 13. A camera accessory that can bedetachably mounted at a camera body, with the camera body comprising afirst cylindrical member provided with an opening of the camera body,and a camera body mount assuming a bayonet structure and including afirst camera body-side tab, a second camera body-side tab and a thirdcamera body-side tab disposed at a circumferential surface of the firstcylindrical member over intervals in a circumferential direction runningalong the circumferential surface, projecting inward from thecircumferential surface along a radial direction, and extending overvarying lengths along the circumferential direction, and a first camerabody-side gap, a second camera body-side gap and a third camerabody-side gap provided between the three camera body-side tabs andextending over varying lengths along the circumferential direction, andwith the camera accessory comprising a second cylindrical member havingan optical path in its inner circumferential side, an accessory mountassuming a bayonet structure with a first accessory-side tab, a secondaccessory-side tab and a third accessory-side tab disposed at acircumferential surface of the second cylindrical member over intervalsin a circumferential direction running along the circumferential surfaceand projecting outward from the circumferential surface along a radialdirection, and a lens, wherein: the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab are disposed at theaccessory mount so that the first accessory-side tab, the secondaccessory-side tab and the third accessory-side tab can be insertedthrough the three camera body-side gaps without any of the firstaccessory-side tab, the second accessory-side tab and the thirdaccessory-side tab being hindered by any of the three camera body-sidetabs when the accessory mount is inserted into the camera body mount ata predetermined interlock position; the first accessory-side tab isdisposed at the accessory mount so that the first accessory-side tab canbe inserted through the first camera body-side gap, having a centralangle of approximately 78.5° which represents a range extending alongthe circumferential direction in the circumferential surface of thefirst cylindrical member, when the accessory mount is inserted into thecamera body mount at the predetermined interlock position; the secondaccessory-side tab is disposed at the accessory mount so that the secondaccessory-side tab can be inserted through the second camera body-sidegap, having a central angle of approximately 61° which represents arange extending along the circumferential direction in thecircumferential surface of the first cylindrical member, when theaccessory mount is inserted into the camera body mount at thepredetermined interlock position; the third accessory-side tab isdisposed at the accessory mount so that the third accessory-side tab canbe inserted through the third camera body-side gap, having a centralangle of approximately 47.5° which represents a range extending alongthe circumferential direction in the circumferential surface of thefirst cylindrical member, when the accessory mount is inserted into thecamera body mount at the predetermined interlock position; the accessorymount includes: a restricting member disposed adjacent to the thirdaccessory-side tab, such that the third accessory-side tab overlaps therestricting member as viewed along a direction parallel to an axialdirection of the camera accessory, and a lock pin hole through which alock pin disposed at the camera body is inserted so as to restrictrotation of the camera accessory relative to the camera body, the lockpin hole being disposed between the first accessory-side tab and thesecond accessory-side tab in the circumferential direction, and beingdisposed closer to the first accessory-side tab than to the secondaccessory-side tab, wherein: the restricting member is disposed at aposition assumed on a side substantially opposite from the lock pin holeacross an optical axis of the lens, and when the first tab, the secondtab and the third tab are inserted at the predetermined interlockposition and completely mounted at the camera body mount, therestricting member and the lock pin hole are disposed substantiallyalong a horizontal axis parallel to a bottom surface of the camera body.14. The camera accessory according to claim 1, wherein: the firstaccessory-side tab is disposed at the accessory mount with a centralangle of a range extending in the circumferential direction beingapproximately 71.5′; the second accessory-side tab is disposed at theaccessory mount with a central angle of a range extending in thecircumferential direction being approximately 58.5′; and the thirdaccessory-side tab is disposed at the accessory mount with a centralangle of a range extending in the circumferential direction beingapproximately 42°.
 15. The camera accessory according to claim 10,wherein: the first accessory-side tab is disposed at the accessory mountwith a central angle of a range extending in the circumferentialdirection of the circumferential surface of the second cylindricalmember being approximately 71.5°; the second accessory-side tab isdisposed at the accessory mount with a central angle of a rangeextending in the circumferential direction in the circumferentialsurface of the second cylindrical member being approximately 58.5°; andthe third accessory-side tab is disposed at the accessory mount with acentral angle of a range extending in the circumferential direction inthe circumferential surface of the second cylindrical member beingapproximately 42°.
 16. The camera accessory according to claim 1,wherein: the camera accessory is a photographic lens to be detachablyengaged with the camera body.
 17. A camera accessory that can bedetachably mounted at a camera body that includes a camera body mount,the camera accessory including an opening forming member that forms anopening defining an optical path in its inner circumferential side andbeing equipped with an accessory mount assuming a bayonet structure witha first tab, a second tab and a third tab disposed at a circumferentialsurface of the opening forming member over intervals in acircumferential direction running along the circumferential surface andprojecting outward from the circumferential surface along aperpendicular direction, wherein: the first tab, the second tab and thethird tab are disposed at the accessory mount so that the first tab, thesecond tab and the third tab can be inserted through the camera bodymount without any of the first tab, the second tab and the third tabbeing hindered by any of three camera body-side tabs at the camera bodymount when the accessory mount is inserted into the camera body mount ata predetermined position in the circumferential direction; the firsttab, the second tab and the third tab extend over varying lengths alongthe circumferential direction; the first tab extends over a greatestlength along the circumferential direction among the first tab, thesecond tab and the third tab; the third tab extends over a smallestlength along the circumferential direction among the first tab, thesecond tab and the third tab; the accessory mount includes: arestricting member, disposed adjacent to the third tab such that thethird tab overlaps the restricting member as viewed along a directionparallel to an axial direction of the camera accessory, that restrictsrotation of the accessory mount relative to the camera body mount in thecircumferential direction; and a lock pin hole through which a lock pindisposed at the camera body is inserted so as to restrict rotation ofthe camera accessory relative to the camera body, the lock pin holebeing disposed between the first tab and the second tab in thecircumferential direction, and being disposed closer to the first tabthan to the second tab, wherein: the restricting member is disposed at aposition assumed on a side substantially opposite from the lock pin holeacross a center of the opening forming member, and when the first tab,the second tab and the third tab are inserted at the predeterminedposition and completely mounted at the camera body mount, therestricting member and the lock pin hole are disposed substantiallyalong a horizontal axis parallel to a bottom surface of the camera body.18. A camera accessory that can be detachably mounted at a camera bodythat includes a camera body mount, the camera accessory including anopening forming member that forms an opening defining an optical path inits inner circumferential side, an accessory mount assuming a bayonetstructure with a first tab, a second tab and a third tab disposed at acircumferential surface of the opening forming member over intervals ina circumferential direction running along the circumferential surfaceand projecting outward from the circumferential surface along aperpendicular direction, and a lens, wherein: the first tab, the secondtab and the third tab are disposed at the accessory mount so that thefirst tab, the second tab and the third tab can be inserted through thecamera body mount without any of the first tab, the second tab and thethird tab being hindered by any of three camera body-side tabs at thecamera body mount, when the accessory mount is inserted into the camerabody mount at a predetermined position in the circumferential direction;the first tab, the second tab and the third tab extend over varyinglengths along the circumferential direction; the first tab extends overa greatest length along the circumferential direction among the firsttab, the second tab and the third tab; the third tab extends over asmallest length along the circumferential direction among the first tab,the second tab and the third tab; the accessory mount includes: arestricting member, disposed adjacent to the third tab such that thethird tab overlaps the restricting member as viewed along a directionparallel to an axial direction of the camera accessory, that restrictsrotation of the accessory mount relative to the camera body mount in thecircumferential direction; and a lock pin hole through which a lock pindisposed at the camera body is inserted so as to restrict rotation ofthe camera accessory relative to the camera body, the lock pin holebeing disposed between the first tab and the second tab in thecircumferential direction, and being disposed closer to the first tabthan to the second tab, wherein: the restricting member is disposed at aposition assumed on a side substantially opposite from the lock pin holeacross an optical axis of the lens, and when the first tab, the secondtab and the third tab are inserted at the predetermined position andcompletely mounted at the camera body mount, the restricting member andthe lock pin hole are disposed substantially along a horizontal axisparallel to a bottom surface of the camera body.
 19. A camera accessorythat can be detachably mounted at a camera body that includes a camerabody mount, the camera accessory including a cylindrical member havingan optical path in its inner circumferential side and being equippedwith an accessory mount assuming a bayonet structure with a first tab, asecond tab and a third tab disposed at a circumferential surface of thecylindrical member over intervals in a circumferential direction runningalong the circumferential surface and projecting outward from thecircumferential surface along a radial direction, wherein: the firsttab, the second tab and the third tab are disposed at the accessorymount so that the first tab, the second tab and the third tab can beinserted through the camera body mount without any of the first tab, thesecond tab and the third tab being hindered by any of three camerabody-side tabs at the camera body mount when the accessory mount isinserted into the camera body mount at a predetermined interlockposition; the first tab, the second tab and the third tab extend overvarying lengths along the circumferential direction; the first tabextends over a greatest length along the circumferential direction amongthe first tab, the second tab and the third tab; the third tab extendsover a smallest length along the circumferential direction among thefirst tab, the second tab and the third tab; the accessory mountincludes: a restricting member disposed adjacent to the third tab suchthat the third tab overlaps the restricting member as viewed along adirection parallel to an axial direction of the camera accessory; and alock pin hole through which a lock pin disposed at the camera body isinserted so as to restrict rotation of the camera accessory relative tothe camera body, the lock pin hole being disposed between the first taband the second tab in the circumferential direction, and being disposedcloser to the first tab than to the second tab, wherein: the restrictingmember is disposed at a position opposite from a position of the lockpin hole.